Configuration Parameters

Descriptions of the Greenplum Database server configuration parameters listed alphabetically.

• add_missing_from
• application_name
• array_nulls
• authentication_timeout
• backslash_quote
• block_size
• bonjour_name
• check_function_bodies
• client_encoding
• client_min_messages
• cpu_index_tuple_cost
• cpu_operator_cost
• cpu_tuple_cost
• cursor_tuple_fraction
• custom_variable_classes
• data_checksums
• DateStyle
• db_user_namespace
• deadlock_timeout
• debug_assertions
• debug_pretty_print
• debug_print_parse
• debug_print_plan
• debug_print_prelim_plan
• debug_print_rewritten
• debug_print_slice_table
• default_statistics_target
• default_tablespace
• default_transaction_isolation
• default_transaction_read_only
• dtx_phase2_retry_count
• dynamic_library_path
• effective_cache_size
• enable_bitmapscan
• enable_groupagg
• enable_hashagg
• enable_hashjoin
• enable_indexscan
• enable_mergejoin
• enable_nestloop
• enable_seqscan
• enable_sort
• enable_tidscan
• escape_string_warning
• explain_pretty_print
• extra_float_digits
• filerep_mirrorvalidation_during_resync
• from_collapse_limit
• gp_adjust_selectivity_for_outerjoins
• gp_analyze_relative_error
• gp_appendonly_compaction
• gp_appendonly_compaction_threshold
• gp_autostats_mode
• gp_autostats_mode_in_functions
• gp_autostats_on_change_threshold
• gp_backup_directIO
• gp_backup_directIO_read_chunk_mb
• gp_cached_segworkers_threshold
• gp_command_count
• gp_connection_send_timeout
• gp_connections_per_thread
• gp_content
• gp_create_table_random_default_distribution
• gp_dbid
• gp_debug_linger
• gp_default_storage_options
• gp_dynamic_partition_pruning
• gp_email_from
• gp_email_smtp_password
• gp_email_smtp_server
• gp_email_smtp_userid
• gp_email_to
• gp_enable_agg_distinct
• gp_enable_agg_distinct_pruning
• gp_enable_direct_dispatch
• gp_enable_exchange_default_partition
• gp_enable_fallback_plan
• gp_enable_fast_sri
• gp_enable_gpperfmon
• gp_enable_groupext_distinct_gather
• gp_enable_groupext_distinct_pruning
• gp_enable_multiphase_agg
• gp_enable_predicate_propagation
• gp_enable_preunique
• gp_enable_relsize_collection
• gp_enable_segment_copy_checking
• gp_enable_sequential_window_plans (Beta)
• gp_enable_sort_distinct
• gp_enable_sort_limit
• gp_external_enable_exec
• gp_external_max_segs
• gp_external_enable_filter_pushdown
• gp_filerep_tcp_keepalives_count
• gp_filerep_tcp_keepalives_idle
• gp_filerep_tcp_keepalives_interval
• gp_fts_probe_interval
• gp_fts_probe_retries
• gp_fts_probe_threadcount
• gp_fts_probe_timeout
• gp_gpperfmon_send_interval
• gpperfmon_log_alert_level
• gp_hadoop_home
• gp_hadoop_target_version
• gp_hashjoin_tuples_per_bucket
• gp_idf_deduplicate
• gp_ignore_error_table
• gp_initial_bad_row_limit
• gp_interconnect_debug_retry_interval
• gp_interconnect_fc_method
• gp_interconnect_hash_multiplier
• gp_interconnect_queue_depth
• gp_interconnect_setup_timeout
• gp_interconnect_snd_queue_depth
• gp_interconnect_type
• gp_log_interconnect
• gp_log_format
• gp_log_fts
• gp_log_interconnect
• gp_log_gang
• gp_max_csv_line_length
• gp_max_databases
• gp_max_filespaces
• gp_max_local_distributed_cache
• gp_max_packet_size
• gp_max_plan_size
• gp_max_slices
• gp_max_tablespaces
• gp_motion_cost_per_row
• gp_num_contents_in_cluster
• gp_recursive_cte_prototype
• gp_reject_percent_threshold
• gp_reraise_signal
• gp_resgroup_memory_policy
• gp_resource_group_bypass
• gp_resource_group_cpu_limit
• gp_resource_group_memory_limit
• gp_resource_manager
• gp_resqueue_memory_policy
• gp_resqueue_priority
• gp_resqueue_priority_cpucores_per_segment
• gp_resqueue_priority_sweeper_interval
• gp_role
• gp_safefswritesize
• gp_segment_connect_timeout
• gp_segments_for_planner
• gp_server_version
• gp_server_version_num
• gp_session_id
• gp_set_proc_affinity
• gp_set_read_only
• gp_snmp_community
• gp_snmp_monitor_address
• gp_snmp_use_inform_or_trap
• gp_statistics_pullup_from_child_partition
• gp_statistics_use_fkeys
• gp_vmem_idle_resource_timeout
• gp_vmem_protect_limit
• gp_vmem_protect_segworker_cache_limit
• gp_workfile_checksumming
• gp_workfile_compress_algorithm
• gp_workfile_limit_files_per_query
• gp_workfile_limit_per_query
• gp_workfile_limit_per_segment
• gpperfmon_port
• ignore_checksum_failure
• integer_datetimes
• IntervalStyle
• join_collapse_limit
• keep_wal_segments
• krb_caseins_users
• krb_server_keyfile
• krb_srvname
• lc_collate
• lc_ctype
• lc_messages
• lc_monetary
• lc_numeric
• lc_time
• listen_addresses
• local_preload_libraries
• log_autostats
• log_connections
• log_disconnections
• log_dispatch_stats
• log_duration
• log_error_verbosity
• log_executor_stats
• log_hostname
• log_min_duration_statement
• log_min_error_statement
• log_min_messages
• log_parser_stats
• log_planner_stats
• log_rotation_age
• log_rotation_size
• log_statement
• log_statement_stats
• log_temp_files
• log_timezone
• log_truncate_on_rotation
• max_appendonly_tables
• max_connections
• max_files_per_process
• max_fsm_pages
• max_fsm_relations
• max_function_args
• max_identifier_length
• max_index_keys
• max_locks_per_transaction
• max_prepared_transactions
• max_resource_portals_per_transaction
• max_resource_queues
• max_stack_depth
• max_statement_mem
• memory_spill_ratio
• optimizer
• optimizer_array_expansion_threshold
• optimizer_analyze_root_partition
• optimizer_control
• optimizer_cost_model
• optimizer_cte_inlining_bound
• optimizer_dpe_stats
• optimizer_enable_associativity
• optimizer_enable_dml
• optimizer_enable_master_only_queries
• optimizer_force_agg_skew_avoidance
• optimizer_force_multistage_agg
• optimizer_force_three_stage_scalar_dqa
• optimizer_join_arity_for_associativity_commutativity
• optimizer_join_order
• optimizer_join_order_threshold
• optimizer_mdcache_size
• optimizer_metadata_caching
• optimizer_minidump
• optimizer_nestloop_factor
• optimizer_parallel_union
• optimizer_penalize_skew
• optimizer_print_missing_stats
• optimizer_print_optimization_stats
• optimizer_sort_factor
• optimizer_use_gpdb_allocators
• optimizer_xform_bind_threshold
• password_hash_algorithm
• pgcrypto.fips
• pgstat_track_activity_query_size
• pljava_classpath
• pljava_classpath_insecure
• pljava_statement_cache_size
• pljava_release_lingering_savepoints
• pljava_vmoptions
• port
• random_page_cost
• readable_external_table_timeout
• repl_catchup_within_range
• replication_timeout
• regex_flavor
• resource_cleanup_gangs_on_wait
• resource_select_only
• runaway_detector_activation_percent
• search_path
• seq_page_cost
• server_encoding
• server_version
• server_version_num
• shared_buffers
• shared_preload_libraries
• ssl
• ssl_ciphers
• standard_conforming_strings
• statement_mem
• statement_timeout
• stats_queue_level
• superuser_reserved_connections
• tcp_keepalives_count
• tcp_keepalives_idle
• tcp_keepalives_interval
• temp_buffers
• TimeZone
• timezone_abbreviations
• track_activities
• track_activity_query_size
• track_counts
• transaction_isolation
• transaction_read_only
• transform_null_equals
• unix_socket_directory
• unix_socket_group
• unix_socket_permissions
• update_process_title
• vacuum_cost_delay
• vacuum_cost_limit
• vacuum_cost_page_dirty
• vacuum_cost_page_hit
• vacuum_cost_page_miss
• vacuum_freeze_min_age
• validate_previous_free_tid
• verify_gpfdists_cert
• vmem_process_interrupt
• wal_receiver_status_interval
• writable_external_table_bufsize
• xid_stop_limit
• xid_warn_limit
• xmlbinary
• xmloption

add_missing_from

Automatically adds missing table references to FROM clauses. Present for compatibility with releases of PostgreSQL prior to 8.1, where this behavior was allowed by default.

application_name 0

Sets the application name for a client session. For example, if connecting via psql, this will be set to psql. Setting an application name allows it to be reported in log messages and statistics views.

array_nulls

This controls whether the array input parser recognizes unquoted NULL as specifying a null array element. By default, this is on, allowing array values containing null values to be entered. Greenplum Database versions before 3.0 did not support null values in arrays, and therefore would treat NULL as specifying a normal array element with the string value ‘NULL’.

authentication_timeout

Maximum time to complete client authentication. This prevents hung clients from occupying a connection indefinitely.

backslash_quote

This controls whether a quote mark can be represented by \‘ in a string literal. The preferred, SQL-standard way to represent a quote mark is by doubling it (‘’) but PostgreSQL has historically also accepted \‘. However, use of \‘ creates security risks because in some client character set encodings, there are multibyte characters in which the last byte is numerically equivalent to ASCII \.

block_size

Reports the size of a disk block.

bonjour_name

Specifies the Bonjour broadcast name. By default, the computer name is used, specified as an empty string. This option is ignored if the server was not compiled with Bonjour support.

check_function_bodies

When set to off, deactivates validation of the function body string during CREATE FUNCTION. Deactivating validation is occasionally useful to avoid problems such as forward references when restoring function definitions from a dump.

client_encoding

Sets the client-side encoding (character set). The default is to use the same as the database encoding. See Supported Character Sets in the PostgreSQL documentation.

client_min_messages

Controls which message levels are sent to the client. Each level includes all the levels that follow it. The later the level, the fewer messages are sent.

cpu_index_tuple_cost

For the legacy query optimizer (planner), sets the estimate of the cost of processing each index row during an index scan. This is measured as a fraction of the cost of a sequential page fetch.

cpu_operator_cost

For the legacy query optimizer (planner), sets the estimate of the cost of processing each operator in a WHERE clause. This is measured as a fraction of the cost of a sequential page fetch.

cpu_tuple_cost

For the legacy query optimizer (planner), Sets the estimate of the cost of processing each row during a query. This is measured as a fraction of the cost of a sequential page fetch.

cursor_tuple_fraction

Tells the legacy query optimizer (planner) how many rows are expected to be fetched in a cursor query, thereby allowing the legacy optimizer to use this information to optimize the query plan. The default of 1 means all rows will be fetched.

custom_variable_classes

Specifies one or several class names to be used for custom variables. A custom variable is a variable not normally known to the server but used by some add-on modules. Such variables must have names consisting of a class name, a dot, and a variable name.

data_checksums

Reports whether checksums are enabled for heap data storage in the database system. Checksums for heap data are activated or deactivated when the database system is initialized and cannot be changed.

Heap data pages store heap tables, catalog tables, indexes, and database metadata. Append-optimized storage has built-in checksum support that is unrelated to this parameter.

Greenplum Database uses checksums to prevent loading data corrupted in the file system into memory managed by database processes. When heap data checksums are enabled, Greenplum Database computes and stores checksums on heap data pages when they are written to disk. When a page is retrieved from disk, the checksum is verified. If the verification fails, an error is generated and the page is not permitted to load into managed memory.

If the ignore_checksum_failure configuration parameter has been set to on, a failed checksum verification generates a warning, but the page is allowed to be loaded into managed memory. If the page is then updated, it is flushed to disk and replicated to the mirror. This can cause data corruption to propagate to the mirror and prevent a complete recovery. Because of the potential for data loss, the ignore_checksum_failure parameter should only be enabled when needed to recover data. See ignore_checksum_failure for more information.

DateStyle

Sets the display format for date and time values, as well as the rules for interpreting ambiguous date input values. This variable contains two independent components: the output format specification and the input/output specification for year/month/day ordering.

db_user_namespace

This enables per-database user names. If on, you should create users as username@dbname. To create ordinary global users, simply append @ when specifying the user name in the client.

deadlock_timeout

The time to wait on a lock before checking to see if there is a deadlock condition. On a heavily loaded server you might want to raise this value. Ideally the setting should exceed your typical transaction time, so as to improve the odds that a lock will be released before the waiter decides to check for deadlock.

debug_assertions

Turns on various assertion checks.

debug_pretty_print

Indents debug output to produce a more readable but much longer output format. client_min_messages or log_min_messages must be DEBUG1 or lower.

debug_print_parse

For each executed query, prints the resulting parse tree. client_min_messages or log_min_messages must be DEBUG1 or lower.

debug_print_plan

For each executed query, prints the Greenplum parallel query execution plan. client_min_messages or log_min_messages must be DEBUG1 or lower.

debug_print_prelim_plan

For each executed query, prints the preliminary query plan. client_min_messages or log_min_messages must be DEBUG1 or lower.

debug_print_rewritten

For each executed query, prints the query rewriter output. client_min_messages or log_min_messages must be DEBUG1 or lower.

debug_print_slice_table

For each executed query, prints the Greenplum query slice plan. client_min_messages or log_min_messages must be DEBUG1 or lower.

default_statistics_target

Sets the default statistics sampling target (the number of values that are stored in the list of common values) for table columns that have not had a column-specific target set via ALTER TABLE SET STATISTICS. Larger values may improve the quality of the legacy query optimizer (planner) estimates.

default_tablespace

The default tablespace in which to create objects (tables and indexes) when a CREATE command does not explicitly specify a tablespace.

default_transaction_isolation

Controls the default isolation level of each new transaction.

default_transaction_read_only

Controls the default read-only status of each new transaction. A read-only SQL transaction cannot alter non-temporary tables.

dtx_phase2_retry_count

The maximum number of retries attempted by Greenplum Database during the second phase of a two phase commit. When one or more segments cannot successfully complete the commit phase, the master retries the commit a maximum of dtx_phase2_retry_count times. If the commit continues to fail on the last retry attempt, the master generates a PANIC.

When the network is unstable, the master may be unable to connect to one or more segments; increasing the number of two phase commit retries may improve high availability of Greenplum when the master encounters transient network issues.

dynamic_library_path

If a dynamically loadable module needs to be opened and the file name specified in the CREATE FUNCTION or LOAD command does not have a directory component (i.e. the name does not contain a slash), the system will search this path for the required file. The compiled-in PostgreSQL package library directory is substituted for $libdir. This is where the modules provided by the standard PostgreSQL distribution are installed.

effective_cache_size

Sets the assumption about the effective size of the disk cache that is available to a single query for the legacy query optimizer (planner). This is factored into estimates of the cost of using an index; a higher value makes it more likely index scans will be used, a lower value makes it more likely sequential scans will be used. This parameter has no effect on the size of shared memory allocated by a Greenplum server instance, nor does it reserve kernel disk cache; it is used only for estimation purposes.

Set this parameter to a number of block_size blocks (default 32K) with no units; for example, 8192 for 256MB. You can also directly specify the size of the effective cache; for example, '1GB' specifies a size of 32768 blocks. The gpconfig utility and SHOW command display the effective cache size value in units such as ‘GB’, ‘MB’, or ‘kB’.

enable_bitmapscan

Activates or deactivates the use of bitmap-scan plan types by the legacy query optimizer (planner). Note that this is different than a Bitmap Index Scan. A Bitmap Scan means that indexes will be dynamically converted to bitmaps in memory when appropriate, giving faster index performance on complex queries against very large tables. It is used when there are multiple predicates on different indexed columns. Each bitmap per column can be compared to create a final list of selected tuples.

enable_groupagg

Activates or deactivates the use of group aggregation plan types by the legacy query optimizer (planner).

enable_hashagg

Activates or deactivates the use of hash aggregation plan types by the legacy query optimizer (planner).

enable_hashjoin

Activates or deactivates the use of hash-join plan types by the legacy query optimizer (planner).

enable_indexscan

Activates or deactivates the use of index-scan plan types by the legacy query optimizer (planner).

enable_mergejoin

Activates or deactivates the use of merge-join plan types by the legacy query optimizer (planner). Merge join is based on the idea of sorting the left- and right-hand tables into order and then scanning them in parallel. So, both data types must be capable of being fully ordered, and the join operator must be one that can only succeed for pairs of values that fall at the ‘same place’ in the sort order. In practice this means that the join operator must behave like equality.

enable_nestloop

Activates or deactivates the use of nested-loop join plans by the legacy query optimizer (planner). It’s not possible to suppress nested-loop joins entirely, but turning this variable off discourages the legacy optimizer from using one if there are other methods available.

enable_seqscan

Activates or deactivates the use of sequential scan plan types by the legacy query optimizer (planner). It’s not possible to suppress sequential scans entirely, but turning this variable off discourages the legacy optimizer from using one if there are other methods available.

enable_sort

Activates or deactivates the use of explicit sort steps by the legacy query optimizer (planner). It’s not possible to suppress explicit sorts entirely, but turning this variable off discourages the legacy optimizer from using one if there are other methods available.

enable_tidscan

Activates or deactivates the use of tuple identifier (TID) scan plan types by the legacy query optimizer (planner).

escape_string_warning

When on, a warning is issued if a backslash (\) appears in an ordinary string literal (‘…’ syntax). Escape string syntax (E’…’) should be used for escapes, because in future versions, ordinary strings will have the SQL standard-conforming behavior of treating backslashes literally.

explain_pretty_print

Determines whether EXPLAIN VERBOSE uses the indented or non-indented format for displaying detailed query-tree dumps.

extra_float_digits

Adjusts the number of digits displayed for floating-point values, including float4, float8, and geometric data types. The parameter value is added to the standard number of digits. The value can be set as high as 3, to include partially-significant digits; this is especially useful for dumping float data that needs to be restored exactly. Or it can be set negative to suppress unwanted digits.

filerep_mirrorvalidation_during_resync

The default setting false improves Greenplum Database performance during incremental resynchronization of segment mirrors. Setting the value to true enables checking for the existence of files for all relations on the segment mirror during incremental resynchronization. Checking for files degrades performance of the incremental resynchronization process but provides a minimal check of database objects.

from_collapse_limit

The legacy query optimizer (planner) will merge sub-queries into upper queries if the resulting FROM list would have no more than this many items. Smaller values reduce planning time but may yield inferior query plans.

gp_adjust_selectivity_for_outerjoins

Enables the selectivity of NULL tests over outer joins.

gp_analyze_relative_error

Sets the estimated acceptable error in the cardinality of the table “ a value of 0.5 is supposed to be equivalent to an acceptable error of 50% (this is the default value used in PostgreSQL). If the statistics collected during ANALYZE are not producing good estimates of cardinality for a particular table attribute, decreasing the relative error fraction (accepting less error) tells the system to sample more rows.

gp_appendonly_compaction

Enables compacting segment files during VACUUM commands. When deactivated, VACUUM only truncates the segment files to the EOF value, as is the current behavior. The administrator may want to deactivate compaction in high I/O load situations or low space situations.

gp_appendonly_compaction_threshold

Specifies the threshold ratio (as a percentage) of hidden rows to total rows that triggers compaction of the segment file when VACUUM is run without the FULL option (a lazy vacuum). If the ratio of hidden rows in a segment file on a segment is less than this threshold, the segment file is not compacted, and a log message is issued.

gp_autostats_mode

Specifies the mode for triggering automatic statistics collection with ANALYZE. The on_no_stats option triggers statistics collection for CREATE TABLE AS SELECT, INSERT, or COPY operations on any table that has no existing statistics.

The on_change option triggers statistics collection only when the number of rows affected exceeds the threshold defined by gp_autostats_on_change_threshold. Operations that can trigger automatic statistics collection with on_change are:

CREATE TABLE AS SELECT

UPDATE

DELETE

INSERT

COPY

Default is on_no_stats.

Note: For partitioned tables, automatic statistics collection is not triggered if data is inserted from the top-level parent table of a partitioned table.

Automatic statistics collection is triggered if data is inserted directly in a leaf table (where the data is stored) of the partitioned table. Statistics are collected only on the leaf table.

gp_autostats_mode_in_functions

Specifies the mode for triggering automatic statistics collection with ANALYZE for statements in procedural language functions. The none option deactivates statistics collection. The on_no_stats option triggers statistics collection for CREATE TABLE AS SELECT, INSERT, or COPY operations that are executed in functions on any table that has no existing statistics.

The on_change option triggers statistics collection only when the number of rows affected exceeds the threshold defined by gp_autostats_on_change_threshold. Operations in functions that can trigger automatic statistics collection with on_change are:

CREATE TABLE AS SELECT

UPDATE

DELETE

INSERT

COPY

gp_autostats_on_change_threshold

Specifies the threshold for automatic statistics collection when gp_autostats_mode is set to on_change. When a triggering table operation affects a number of rows exceeding this threshold, ANALYZEis added and statistics are collected for the table.

gp_backup_directIO

Direct I/O allows Greenplum Database to bypass the buffering of memory within the file system cache for backup. When Direct I/O is used for a file, data is transferred directly from the disk to the application buffer, without the use of the file buffer cache.

Direct I/O is supported only on Red Hat Enterprise Linux, CentOS, and SUSE.

gp_backup_directIO_read_chunk_mb

Sets the chunk size in MB when Direct I/O is enabled with gp_backup_directIO. The default chunk size is 20MB.

The default value is the optimal setting. Decreasing it will increase the backup time and increasing it will result in little change to backup time.

gp_cached_segworkers_threshold

When a user starts a session with Greenplum Database and issues a query, the system creates groups or ‘gangs’ of worker processes on each segment to do the work. After the work is done, the segment worker processes are destroyed except for a cached number which is set by this parameter. A lower setting conserves system resources on the segment hosts, but a higher setting may improve performance for power-users that want to issue many complex queries in a row.

gp_command_count

Shows how many commands the master has received from the client. Note that a single SQLcommand might actually involve more than one command internally, so the counter may increment by more than one for a single query. This counter also is shared by all of the segment processes working on the command.

gp_connection_send_timeout

Timeout for sending data to unresponsive Greenplum Database user clients during query processing. A value of 0 deactivates the timeout, Greenplum Database waits indefinitely for a client. When the timeout is reached, the query is cancelled with this message:

Could not send data to client: Connection timed out.

gp_connections_per_thread

Controls the number of asynchronous threads (worker threads) that a Greenplum Database query dispatcher (QD) generates when dispatching work to query executor processes on segment instances when processing SQL queries. The value sets the number of primary segment instances that a worker thread connects to when processing a query. For example, when the value is 2 and there are 64 segment instances, a QD generates 32 worker threads to dispatch a query plan work. Each thread is assigned to two segments.

For the default value, 0, a query dispatcher generates two types of threads: a main thread that manages the dispatch of query plan work, and an interconnect thread. The main thread also acts as a worker thread.

For a value greater than 0, a QD generates three types of threads: a main thread, one or more worker threads, and an interconnect thread. When the value is equal to or greater than the number of segment instances, a QD generates three threads: a main thread, a single worker thread, and an interconnect thread.

The value does not need to be changed from the default unless there are known throughput performance issues.

This parameter is master only and changing it requires a server restart.

gp_content

The local content id if a segment.

gp_create_table_random_default_distribution

Controls table creation when a Greenplum Database table is created with a CREATE TABLE or CREATE TABLE AS command that does not contain a DISTRIBUTED BY clause.

For CREATE TABLE, if the value of the parameter is off (the default), and the table creation command does not contain a DISTRIBUTED BY clause, Greenplum Database chooses the table distribution key based on the command. If the LIKE or INHERITS clause is specified in table creation command, the created table uses the same distribution key as the source or parent table.

If the value of the parameter is set to on, Greenplum Database follows these rules to create a table when the DISTRIBUTED BY clause is not specified:

• If PRIMARY KEY or UNIQUE columns are not specified, the distribution of the table is random (DISTRIBUTED RANDOMLY). Table distribution is random even if the table creation command contains the LIKE or INHERITS clause.
• If PRIMARY KEY or UNIQUE columns are specified, a DISTRIBUTED BY clause must also be specified. If a DISTRIBUTED BY clause is not specified as part of the table creation command, the command fails.

For a CREATE TABLE AS command that does not contain a distribution clause:

• If the legacy query optimizer creates the table, and the value of the parameter is off, the table distribution policy is determined based on the command.
• If the legacy query optimizer creates the table, and the value of the parameter is on, the table distribution policy is random.
• If GPORCA creates the table, the table distribution policy is random. The parameter value has no affect.

For information about the legacy query optimizer and GPORCA, see “Querying Data” in the Greenplum Database Administrator Guide.

gp_dbid

The local content dbid if a segment.

gp_debug_linger

Number of seconds for a Greenplum process to linger after a fatal internal error.

gp_default_storage_options

Set the default values for the following table storage options when a table is created with the CREATE TABLE command.

• APPENDONLY
• BLOCKSIZE
• CHECKSUM
• COMPRESSTYPE
• COMPRESSLEVEL
• ORIENTATION

Specify multiple storage option values as a comma separated list.

You can set the storage options with this parameter instead of specifying the table storage options in the WITH of the CREATE TABLE command. The table storage options that are specified with the CREATE TABLE command override the values specified by this parameter.

Not all combinations of storage option values are valid. If the specified storage options are not valid, an error is returned. See the CREATE TABLE command for information about table storage options.

The defaults can be set for a database and user. If the server configuration parameter is set at different levels, this the order of precedence, from highest to lowest, of the table storage values when a user logs into a database and creates a table:

1. The values specified in a CREATE TABLE command with the WITH clause or ENCODING clause
2. The value of gp_default_storage_options that set for the user with the ALTER ROLE…SET command
3. The value of gp_default_storage_options that is set for the database with the ALTER DATABASE…SET command
4. The value of gp_default_storage_options that is set for the Greenplum Database system with the gpconfig utility

The parameter value is not cumulative. For example, if the parameter specifies the APPENDONLY and COMPRESSTYPE options for a database and a user logs in and sets the parameter to specify the value for the ORIENTATION option, the APPENDONLY, and COMPRESSTYPE values set at the database level are ignored.

This example ALTER DATABASE command sets the default ORIENTATION and COMPRESSTYPE table storage options for the database mystest.

ALTER DATABASE mytest SET gp_default_storage_options = 'orientation=column, compresstype=rle_type'

To create an append-optimized table in the mytest database with column-oriented table and RLE compression. The user needs to specify only APPENDONLY=TRUE in the WITH clause.

This example gpconfig utility command sets the default storage option for a Greenplum Database system. If you set the defaults for multiple table storage options, the value must be enclosed in single quotes.

gpconfig -c 'gp_default_storage_options' -v 'appendonly=true, orientation=column'

This example gpconfig utility command shows the value of the parameter. The parameter value must be consistent across the Greenplum Database master and all segments.

gpconfig -s 'gp_default_storage_options'

Note: 1The set classification when the parameter is set at the system level with the gpconfig utility.

Note: 2QuickLZ compression is available only in the commercial release of Tanzu Greenplum.

gp_dynamic_partition_pruning

Enables plans that can dynamically eliminate the scanning of partitions.

gp_email_from

The email address used to send email alerts, in the format of:

'username@example.com'

or

'Name <username@example.com>'

gp_email_smtp_password

The password/passphrase used to authenticate with the SMTP server.

gp_email_smtp_server

The fully qualified domain name or IP address and port of the SMTP server to use to send the email alerts. Must be in the format of:

smtp_servername.domain.com:port

gp_email_smtp_userid

The user id used to authenticate with the SMTP server.

gp_email_to

A semi-colon (;) separated list of email addresses to receive email alert messages to in the format of: 'username@example.com'

or

'Name <username@example.com>'

If this parameter is not set, then email alerts are deactivated.

gp_enable_agg_distinct

Activates or deactivates two-phase aggregation to compute a single distinct-qualified aggregate. This applies only to subqueries that include a single distinct-qualified aggregate function.

gp_enable_agg_distinct_pruning

Activates or deactivates three-phase aggregation and join to compute distinct-qualified aggregates. This applies only to subqueries that include one or more distinct-qualified aggregate functions.

gp_enable_direct_dispatch

Activates or deactivates the dispatching of targeted query plans for queries that access data on a single segment. When on, queries that target rows on a single segment will only have their query plan dispatched to that segment (rather than to all segments). This significantly reduces the response time of qualifying queries as there is no interconnect setup involved. Direct dispatch does require more CPU utilization on the master.

gp_enable_exchange_default_partition

Controls availability of the EXCHANGE DEFAULT PARTITION clause for ALTER TABLE. The default value for the parameter is off. The clause is not available and Greenplum Database returns an error if the clause is specified in an ALTER TABLE command.

If the value is on, Greenplum Database returns a warning stating that exchanging the default partition might result in incorrect results due to invalid data in the default partition.

Warning: Before you exchange the default partition, you must ensure the data in the table to be exchanged, the new default partition, is valid for the default partition. For example, the data in the new default partition must not contain data that would be valid in other leaf child partitions of the partitioned table. Otherwise, queries against the partitioned table with the exchanged default partition that are executed by GPORCA might return incorrect results.

gp_enable_fallback_plan

Allows use of deactivated plan types when a query would not be feasible without them.

gp_enable_fast_sri

When set to on, the legacy query optimizer (planner) plans single row inserts so that they are sent directly to the correct segment instance (no motion operation required). This significantly improves performance of single-row-insert statements.

gp_enable_gpperfmon

Activates or deactivates the data collection agents that populate the gpperfmon database for Greenplum Command Center.

gp_enable_groupext_distinct_gather

Activates or deactivates gathering data to a single node to compute distinct-qualified aggregates on grouping extension queries. When this parameter and gp_enable_groupext_distinct_pruning are both enabled, the legacy query optimizer (planner) uses the cheaper plan.

gp_enable_groupext_distinct_pruning

Activates or deactivates three-phase aggregation and join to compute distinct-qualified aggregates on grouping extension queries. Usually, enabling this parameter generates a cheaper query plan that the legacy query optimizer (planner) will use in preference to existing plan.

gp_enable_multiphase_agg

Activates or deactivates the use of two or three-stage parallel aggregation plans legacy query optimizer (planner). This approach applies to any subquery with aggregation. If gp_enable_multiphase_agg is off, thengp_enable_agg_distinct and gp_enable_agg_distinct_pruning are deactivated.

gp_enable_predicate_propagation

When enabled, the legacy query optimizer (planner) applies query predicates to both table expressions in cases where the tables are joined on their distribution key column(s). Filtering both tables prior to doing the join (when possible) is more efficient.

gp_enable_preunique

Enables two-phase duplicate removal for SELECT DISTINCT queries (not SELECT COUNT(DISTINCT)). When enabled, it adds an extra SORT DISTINCT set of plan nodes before motioning. In cases where the distinct operation greatly reduces the number of rows, this extra SORT DISTINCT is much cheaper than the cost of sending the rows across the Interconnect.

gp_enable_relsize_collection

Enables GPORCA and the legacy query optimizer (planner) to use the estimated size of a table (pg_relation_size function) if there are no statistics for the table. By default, GPORCA and the planner use a default value to estimate the number of rows if statistics are not available. The default behavior improves query optimization time and reduces resource queue usage in heavy workloads, but can lead to suboptimal plans.

This parameter is ignored for a root partition of a partitioned table. When GPORCA is enabled and the root partition does not have statistics, GPORCA always uses the default value. You can use ANALZYE ROOTPARTITION to collect statistics on the root partition. See ANALYZE.

gp_enable_sequential_window_plans (Beta)

If on, enables non-parallel (sequential) query plans for queries containing window function calls. If off, evaluates compatible window functions in parallel and rejoins the results. This is a Beta feature.

gp_enable_segment_copy_checking

Controls whether the distribution policy for a table (from the table DISTRIBUTED clause) is checked when data is copied into the table with the COPY FROM...ON SEGMENT command. The default is true, check the policy when copying data into the table. An error is returned in these situations.

• For a table that is not a partitioned table, an error is returned if the row of data violates the distribution policy for a segment instance.
• For a partitioned table, an error is returned if either of the following is true.
  • If the distribution policy of the child leaf partitioned table is the same as the root table and the row of data violates the distribution policy for a segment instance.
  • If the distribution policy of the child leaf partitioned table is not the same as the root table.

If the value is false, the distribution policy is not checked. The data added to the table might violate the table distribution policy for the segment instance. Manual redistribution of table data might be required. See the ALTER TABLE clause WITH REORGANIZE.

The parameter can be set for a database system or a session. The parameter cannot be set for a specific database.

gp_enable_sort_distinct

Enable duplicates to be removed while sorting.

gp_enable_sort_limit

Enable LIMIT operation to be performed while sorting. Sorts more efficiently when the plan requires the first limit_number of rows at most.

gp_external_enable_exec

Activates or deactivates the use of external tables that execute OS commands or scripts on the segment hosts (CREATE EXTERNAL TABLE EXECUTE syntax). Must be enabled if using the Command Center or MapReduce features.

gp_external_max_segs

Sets the number of segments that will scan external table data during an external table operation, the purpose being not to overload the system with scanning data and take away resources from other concurrent operations. This only applies to external tables that use the gpfdist:// protocol to access external table data.

gp_external_enable_filter_pushdown

Enable filter pushdown when reading data from external tables. If pushdown fails, a query is executed without pushing filters to the external data source (instead, Greenplum Database applies the same constraints to the result). See Defining External Tables for more information.

gp_filerep_tcp_keepalives_count

How many keepalives may be lost before the connection is considered dead. A value of 0 uses the system default. If TCP_KEEPCNT is not supported, this parameter must be 0.

Use this parameter for all connections that are between a primary and mirror segment. Use tcp_keepalives_count for settings that are not between a primary and mirror segment.

gp_filerep_tcp_keepalives_idle

Number of seconds between sending keepalives on an otherwise idle connection. A value of 0 uses the system default. If TCP_KEEPIDLE is not supported, this parameter must be 0.

Use this parameter for all connections that are between a primary and mirror segment. Use tcp_keepalives_idle for settings that are not between a primary and mirror segment.

gp_filerep_tcp_keepalives_interval

How many seconds to wait for a response to a keepalive before retransmitting. A value of 0 uses the system default. If TCP_KEEPINTVL is not supported, this parameter must be 0.

Use this parameter for all connections that are between a primary and mirror segment. Use tcp_keepalives_interval for settings that are not between a primary and mirror segment.

gp_fts_probe_interval

Specifies the polling interval for the fault detection process (ftsprobe). The ftsprobe process will take approximately this amount of time to detect a segment failure.

gp_fts_probe_retries

Specifies the number of times the fault detection process (ftsprobe) attempts to connect to a segment before reporting segment failure.

gp_fts_probe_threadcount

Specifies the number of ftsprobe threads to create. This parameter should be set to a value equal to or greater than the number of segments per host.

gp_fts_probe_timeout

Specifies the allowed timeout for the fault detection process (ftsprobe) to establish a connection to a segment before declaring it down.

gp_log_fts

Controls the amount of detail the fault detection process (ftsprobe) writes to the log file.

gp_log_interconnect

Controls the amount of information that is written to the log file about communication between Greenplum Database segment instance worker processes. The default value is terse. The log information is written to both the master and segment instance logs.

Increasing the amount of logging could affect performance and increase disk space usage.

gp_log_gang

Controls the amount of information that is written to the log file about query worker process creation and query management. The default value is OFF, do not log information.

gp_gpperfmon_send_interval

Sets the frequency that the Greenplum Database server processes send query execution updates to the data collection agent processes used to populate the gpperfmon database for Command Center. Query operations executed during this interval are sent through UDP to the segment monitor agents. If you find that an excessive number of UDP packets are dropped during long-running, complex queries, you may consider increasing this value.

gpperfmon_log_alert_level

Controls which message levels are written to the gpperfmon log. Each level includes all the levels that follow it. The later the level, the fewer messages are sent to the log.

Note: If the gpperfmon database is installed and is monitoring the database, the default value is warning.

gp_hadoop_home

Specifies the installation directory for the Greenplum Database gphdfs protocol (deprecated) Hadoop target.

gp_hadoop_target_version

The installed version of the Greenplum Database gphdfs protocol (deprecated) Hadoop target.

gp_hashjoin_tuples_per_bucket

Sets the target density of the hash table used by HashJoin operations. A smaller value will tend to produce larger hash tables, which can increase join performance.

gp_idf_deduplicate

Changes the strategy to compute and process MEDIAN, and PERCENTILE_DISC.

gp_ignore_error_table

Controls Greenplum Database behavior when the INTO ERROR TABLE clause is specified in a CREATE EXTERNAL TABLE or COPY command. The INTO ERROR TABLE clause was removed in Greenplum Database 5.

The default value is false, Greenplum Database returns an error if the INTO ERROR TABLE clause is specified in a command.

If the value is true, Greenplum Database ignores the clause, issues a warning, and executes the command without the INTO ERROR TABLE clause. In Greenplum Database 5.x and later, you access the error log information with built-in SQL functions. See the CREATE EXTERNAL TABLE or COPY command.

You can set this value to true to avoid the Greenplum Database error when you run applications that execute CREATE EXTERNAL TABLE or COPY commands that include the Greenplum Database 4.3.x INTO ERROR TABLE clause.

gp_initial_bad_row_limit

For the parameter value n, Greenplum Database stops processing input rows when you import data with the COPY command or from an external table if the first n rows processed contain formatting errors. If a valid row is processed within the first n rows, Greenplum Database continues processing input rows.

Setting the value to 0 deactivates this limit.

The SEGMENT REJECT LIMIT clause can also be specified for the COPY command or the external table definition to limit the number of rejected rows.

INT_MAX is the largest value that can be stored as an integer on your system.

gp_interconnect_debug_retry_interval

Specifies the interval, in seconds, to log Greenplum Database interconnect debugging messages when the server configuration parameter gp_log_interconnect is set to DEBUG. The default is 10 seconds.

The log messages contain information about the interconnect communication between Greenplum Database segment instance worker processes. The information can be helpful when debugging network issues between segment instances.

gp_interconnect_fc_method

Specifies the flow control method used for the default Greenplum Database UDPIFC interconnect.

For capacity based flow control, senders do not send packets when receivers do not have the capacity.

Loss based flow control is based on capacity based flow control, and also tunes the sending speed according to packet losses.

gp_interconnect_hash_multiplier

Sets the size of the hash table used by the Greenplum Database to track interconnect connections with the default UDPIFC interconnect. This number is multiplied by the number of segments to determine the number of buckets in the hash table. Increasing the value may increase interconnect performance for complex multi-slice queries (while consuming slightly more memory on the segment hosts).

gp_interconnect_queue_depth

Sets the amount of data per-peer to be queued by the Greenplum Database interconnect on receivers (when data is received but no space is available to receive it the data will be dropped, and the transmitter will need to resend it) for the default UDPIFC interconnect. Increasing the depth from its default value will cause the system to use more memory, but may increase performance. It is reasonable to set this value between 1 and 10. Queries with data skew potentially perform better with an increased queue depth. Increasing this may radically increase the amount of memory used by the system.

gp_interconnect_setup_timeout

Specifies the amount of time, in seconds, that Greenplum Database waits for the interconnect to complete setup before it times out.

gp_interconnect_snd_queue_depth

Sets the amount of data per-peer to be queued by the default UDPIFC interconnect on senders. Increasing the depth from its default value will cause the system to use more memory, but may increase performance. Reasonable values for this parameter are between 1 and 4. Increasing the value might radically increase the amount of memory used by the system.

gp_interconnect_transmit_timeout

Specifies the amount of time, in seconds, that Greenplum Database waits for network transmission of interconnect traffic to complete before it times out.

gp_interconnect_type

Sets the networking protocol used for Greenplum Database interconnect traffic. UDPIFC specifies using UDP with flow control for interconnect traffic, and is the only value supported.

UDPIFC (the default) specifies using UDP with flow control for interconnect traffic. Specify the interconnect flow control method with gp_interconnect_fc_method.

With TCP as the interconnect protocol, Greenplum Database has an upper limit of 1000 segment instances - less than that if the query workload involves complex, multi-slice queries.

gp_log_format

Specifies the format of the server log files. If using gp_toolkit administrative schema, the log files must be in CSV format.

gp_max_csv_line_length

The maximum length of a line in a CSV formatted file that will be imported into the system. The default is 1MB (1048576 bytes). Maximum allowed is 1GB (1073741824 bytes). The default may need to be increased if using the gp_toolkit administrative schema to read Greenplum Database log files.

Note: This parameter is deprecated and will be removed in a future release.

gp_max_databases

The maximum number of databases allowed in a Greenplum Database system.

gp_max_filespaces

The maximum number of filespaces allowed in a Greenplum Database system.

gp_max_local_distributed_cache

Sets the maximum number of distributed transaction log entries to cache in the backend process memory of a segment instance.

The log entries contain information about the state of rows that are being accessed by an SQL statement. The information is used to determine which rows are visible to an SQL transaction when executing multiple simultaneous SQL statements in an MVCC environment. Caching distributed transaction log entries locally improves transaction processing speed by improving performance of the row visibility determination process.

The default value is optimal for a wide variety of SQL processing environments.

gp_max_packet_size

Sets the tuple-serialization chunk size for the Greenplum Database interconnect.

gp_max_plan_size

Specifies the total maximum uncompressed size of a query execution plan multiplied by the number of Motion operators (slices) in the plan. If the size of the query plan exceeds the value, the query is cancelled and an error is returned. A value of 0 means that the size of the plan is not monitored.

You can specify a value in kB, MB, or GB. The default unit is kB. For example, a value of 200 is 200kB. A value of 1GB is the same as 1024MB or 1048576kB.

gp_max_slices

Specifies the maximum number of slices (portions of a query plan that are executed on segment instances) that can be generated by a query. If the query generates more than the specified number of slices, Greenplum Database returns an error and does not execute the query. The default value is 0, no maximum value.

Executing a query that generates a large number of slices might affect Greenplum Database performance. For example, a query that contains UNION or UNION ALL operators over several complex views can generate a large number of slices. You can run EXPLAIN ANALYZE on the query to view slice statistics for the query.

gp_max_tablespaces

The maximum number of tablespaces allowed in a Greenplum Database system.

gp_motion_cost_per_row

Sets the legacy query optimizer (planner) cost estimate for a Motion operator to transfer a row from one segment to another, measured as a fraction of the cost of a sequential page fetch. If 0, then the value used is two times the value of cpu_tuple_cost.

gp_num_contents_in_cluster

The number of primary segments in the Greenplum Database system.

gp_recursive_cte_prototype

Controls the availability of the RECURSIVE keyword (Beta) in the WITH clause of a SELECT[ INTO] command. The keyword allows a subquery in the WITH clause of a SELECT[ INTO] command to reference itself. The default value is false, the keyword is not allowed in the WITH clause a SELECT[ INTO] command.

Note: The RECURSIVE keyword is a Beta feature.

For information about the RECURSIVE keyword (Beta), see the SELECT command.

The parameter can be set for a database system, an individual database, or a session or query.

Note: This parameter will be removed if the RECURSIVE keyword is promoted from Beta or if the keyword is removed from Greenplum Database.

gp_reject_percent_threshold

For single row error handling on COPY and external table SELECTs, sets the number of rows processed before SEGMENT REJECT LIMIT n PERCENT starts calculating.

gp_reraise_signal

If enabled, will attempt to dump core if a fatal server error occurs.

gp_resgroup_memory_policy

Note: The gp_resgroup_memory_policy server configuration parameter is enforced only when resource group-based resource management is active.

Used by a resource group to manage memory allocation to query operators.

When set to auto, Greenplum Database uses resource group memory limits to distribute memory across query operators, allocating a fixed size of memory to non-memory-intensive operators and the rest to memory-intensive operators.

When you specify eager_free, Greenplum Database distributes memory among operators more optimally by re-allocating memory released by operators that have completed their processing to operators in a later query stage.

gp_resource_group_bypass

Note: The gp_resource_group_bypass server configuration parameter is enforced only when resource group-based resource management is active.

Activates or deactivates the enforcement of resource group concurrent transaction limits on Greenplum Database resources. The default value is false, which enforces resource group transaction limits. Resource groups manage resources such as CPU, memory, and the number of concurrent transactions that are used by queries and external components such as PL/Container.

You can set this parameter to true to bypass resource group concurrent transaction limitations so that a query can run immediately. For example, you can set the parameter to true for a session to run a system catalog query or a similar query that requires a minimal amount of resources.

When you set this parameter to true and a run a query, the query runs in this environment:

• The query runs inside a resource group. The resource group assignment for the query does not change.
• The query memory quota is approximately 10 MB per query. The memory is allocated from resource group shared memory or global shared memory. The query fails if there is not enough shared memory available to fulfill the memory allocation request.

This parameter can be set for a session. The parameter cannot be set within a transaction or a function.

gp_resource_group_cpu_limit

Note: The gp_resource_group_cpu_limit server configuration parameter is enforced only when resource group-based resource management is active.

Identifies the maximum percentage of system CPU resources to allocate to resource groups on each Greenplum Database segment node.

gp_resource_group_memory_limit

Note: The gp_resource_group_memory_limit server configuration parameter is enforced only when resource group-based resource management is active.

Identifies the maximum percentage of system memory resources to allocate to resource groups on each Greenplum Database segment node.

Note: When resource group-based resource management is active, the memory allotted to a segment host is equally shared by active primary segments. Greenplum Database assigns memory to primary segments when the segment takes the primary role. The initial memory allotment to a primary segment does not change, even in a failover situation. This may result in a segment host utilizing more memory than the gp_resource_group_memory_limit setting permits.

For example, suppose your Greenplum Database cluster is utilizing the default gp_resource_group_memory_limit of 0.7 and a segment host named seghost1 has 4 primary segments and 4 mirror segments. Greenplum Database assigns each primary segment on seghost1 (0.7 / 4 = 0.175%) of overall system memory. If failover occurs and two mirrors on seghost1 fail over to become primary segments, each of the original 4 primaries retain their memory allotment of 0.175, and the two new primary segments are each allotted (0.7 / 6 = 0.116%) of system memory. seghost1‘s overall memory allocation in this scenario is

0.7 + (0.116 * 2) = 0.932%

which is above the percentage configured in the gp_resource_group_memory_limit setting.

gp_resource_manager

Identifies the resource management scheme currently enabled in the Greenplum Database cluster. The default scheme is to use resource queues. For information about Greenplum Database resource management, see Managing Resources.

gp_resqueue_memory_policy

Note: The gp_resqueue_memory_policy server configuration parameter is enforced only when resource queue-based resource management is active.

Enables Greenplum memory management features. The distribution algorithm eager_free takes advantage of the fact that not all operators execute at the same time(in Greenplum Database 4.2 and later). The query plan is divided into stages and Greenplum Database eagerly frees memory allocated to a previous stage at the end of that stage’s execution, then allocates the eagerly freed memory to the new stage.

When set to none, memory management is the same as in Greenplum Database releases prior to 4.1.

When set to auto, query memory usage is controlled by statement_mem and resource queue memory limits.

gp_resqueue_priority

Note: The gp_resqueue_priority server configuration parameter is enforced only when resource queue-based resource management is active.

Activates or deactivates query prioritization. When this parameter is deactivated, existing priority settings are not evaluated at query run time.

gp_resqueue_priority_cpucores_per_segment

Note: The gp_resqueue_priority_cpucores_per_segment server configuration parameter is enforced only when resource queue-based resource management is active.

Specifies the number of CPU units allocated per segment instance. For example, if a Greenplum Database cluster has 10-core segment hosts that are configured with four segments, set the value for the segment instances to 2.5. For the master instance, the value would be 10. A master host typically has only the master instance running on it, so the value for the master should reflect the usage of all available CPU cores.

Incorrect settings can result in CPU under-utilization or query prioritization not working as designed.

The default values for the Greenplum Data Computing Appliance are 4 for segments and 4 for the master.

gp_resqueue_priority_sweeper_interval

Note: The gp_resqueue_priority_sweeper_interval server configuration parameter is enforced only when resource queue-based resource management is active.

Specifies the interval at which the sweeper process evaluates current CPU usage. When a new statement becomes active, its priority is evaluated and its CPU share determined when the next interval is reached.

gp_role

The role of this server process “ set to dispatch for the master and execute for a segment.

gp_safefswritesize

Specifies a minimum size for safe write operations to append-optimized tables in a non-mature file system. When a number of bytes greater than zero is specified, the append-optimized writer adds padding data up to that number in order to prevent data corruption due to file system errors. Each non-mature file system has a known safe write size that must be specified here when using Greenplum Database with that type of file system. This is commonly set to a multiple of the extent size of the file system; for example, Linux ext3 is 4096 bytes, so a value of 32768 is commonly used.

gp_segment_connect_timeout

Time that the Greenplum interconnect will try to connect to a segment instance over the network before timing out. Controls the network connection timeout between master and primary segments, and primary to mirror segment replication processes.

gp_segments_for_planner

Sets the number of primary segment instances for the legacy query optimizer (planner) to assume in its cost and size estimates. If 0, then the value used is the actual number of primary segments. This variable affects the legacy optimizer’s estimates of the number of rows handled by each sending and receiving process in Motion operators.

gp_server_version

Reports the version number of the server as a string. A version modifier argument might be appended to the numeric portion of the version string, example: 5.0.0 beta.

gp_server_version_num

Reports the version number of the server as an integer. The number is guaranteed to always be increasing for each version and can be used for numeric comparisons. The major version is represented as is, the minor and patch versions are zero-padded to always be double digit wide.

gp_session_id

A system assigned ID number for a client session. Starts counting from 1 when the master instance is first started.

gp_set_proc_affinity

If enabled, when a Greenplum server process (postmaster) is started it will bind to a CPU.

gp_set_read_only

Set to on to deactivate writes to the database. Any in progress transactions must finish before read-only mode takes affect.

gp_snmp_community

Set to the community name you specified for your environment.

gp_snmp_monitor_address

The hostname:port of your network monitor application. Typically, the port number is 162. If there are multiple monitor addresses, separate them with a comma.

gp_snmp_use_inform_or_trap

Trap notifications are SNMP messages sent from one application to another (for example, between Greenplum Database and a network monitoring application). These messages are unacknowledged by the monitoring application, but generate less network overhead.

Inform notifications are the same as trap messages, except that the application sends an acknowledgement to the application that generated the alert.

gp_statistics_pullup_from_child_partition

Enables the use of statistics from child tables when planning queries on the parent table by the legacy query optimizer (planner).

gp_statistics_use_fkeys

When enabled, allows the legacy query optimizer (planner) to use foreign key information stored in the system catalog to optimize joins between foreign keys and primary keys.

gp_vmem_idle_resource_timeout

If a database session is idle for longer than the time specified, the session will free system resources (such as shared memory), but remain connected to the database. This allows more concurrent connections to the database at one time.

gp_vmem_protect_limit

Note: The gp_vmem_protect_limit server configuration parameter is enforced only when resource queue-based resource management is active.

Sets the amount of memory (in number of MBs) that all postgres processes of an active segment instance can consume. If a query causes this limit to be exceeded, memory will not be allocated and the query will fail. Note that this is a local parameter and must be set for every segment in the system (primary and mirrors). When setting the parameter value, specify only the numeric value. For example, to specify 4096MB, use the value 4096. Do not add the units MB to the value.

To prevent over-allocation of memory, these calculations can estimate a safe gp_vmem_protect_limit value.

First calculate the value gp_vmem. This is the Greenplum Database memory available on a host.

• If the total system memory is less than 256 GB, use this formula:

  <gp_vmem> = ((<SWAP> + <RAM>) – (7.5GB + 0.05 * <RAM>)) / 1.7

• If the total system memory is equal to or greater than 256 GB, use this formula:

  <gp_vmem> = ((<SWAP> + <RAM>) – (7.5GB + 0.05 * <RAM>)) / 1.17

where SWAP is the host swap space and RAM is the RAM on the host in GB.

Next, calculate the max_acting_primary_segments. This is the maximum number of primary segments that can be running on a host when mirror segments are activated due to a failure. With mirrors arranged in a 4-host block with 8 primary segments per host, for example, a single segment host failure would activate two or three mirror segments on each remaining host in the failed host’s block. The max_acting_primary_segments value for this configuration is 11 (8 primary segments plus 3 mirrors activated on failure).

This is the calculation for gp_vmem_protect_limit. The value should be converted to MB.

`gp_vmem_protect_limit` = <gp_vmem> / <acting_primary_segments>

For scenarios where a large number of workfiles are generated, this is the calculation for gp_vmem that accounts for the workfiles.

• If the total system memory is less than 256 GB:

  gp_vmem = ((SWAP + RAM) – (7.5GB + 0.05 * RAM - (300KB * <total_#_workfiles>))) / 1.7

• If the total system memory is equal to or greater than 256 GB:

  gp_vmem = ((SWAP + RAM) – (7.5GB + 0.05 * RAM - (300KB * <total_#_workfiles>))) / 1.17

For information about monitoring and managing workfile usage, see the Greenplum Database Administrator Guide.

Based on the gp_vmem value you can calculate the value for the vm.overcommit_ratio operating system kernel parameter. This parameter is set when you configure each Greenplum Database host.

vm.overcommit_ratio = (<RAM> - (0.026 * <gp_vmem>)) / <RAM>

Note: The default value for the kernel parameter vm.overcommit_ratio in Red Hat Enterprise Linux is 50.

For information about the kernel parameter, see the Greenplum Database Installation Guide.

gp_vmem_protect_segworker_cache_limit

If a query executor process consumes more than this configured amount, then the process will not be cached for use in subsequent queries after the process completes. Systems with lots of connections or idle processes may want to reduce this number to free more memory on the segments. Note that this is a local parameter and must be set for every segment.

gp_workfile_checksumming

Adds a checksum value to each block of a work file (or spill file) used by HashAgg and HashJoin query operators. This adds an additional safeguard from faulty OS disk drivers writing corrupted blocks to disk. When a checksum operation fails, the query will cancel and rollback rather than potentially writing bad data to disk.

gp_workfile_compress_algorithm

When a hash aggregation or hash join operation spills to disk during query processing, specifies the compression algorithm to use on the spill files. If using zlib, the zlib library must be installed on all hosts in the Greenplum Database cluster.

If your Greenplum Database installation uses serial ATA (SATA) disk drives, setting the value of this parameter to zlib might help to avoid overloading the disk subsystem with IO operations.

gp_workfile_limit_files_per_query

Sets the maximum number of temporary spill files (also known as workfiles) allowed per query per segment. Spill files are created when executing a query that requires more memory than it is allocated. The current query is terminated when the limit is exceeded.

Set the value to 0 (zero) to allow an unlimited number of spill files. master session reload

gp_workfile_limit_per_query

Sets the maximum disk size an individual query is allowed to use for creating temporary spill files at each segment. The default value is 0, which means a limit is not enforced.

gp_workfile_limit_per_segment

Sets the maximum total disk size that all running queries are allowed to use for creating temporary spill files at each segment. The default value is 0, which means a limit is not enforced.

gpperfmon_port

Sets the port on which all data collection agents (for Command Center) communicate with the master.

ignore_checksum_failure

Only has effect if data_checksums is enabled.

Greenplum Database uses checksums to prevent loading data that has been corrupted in the file system into memory managed by database processes.

By default, when a checksum verify error occurs when reading a heap data page, Greenplum Database generates an error and prevents the page from being loaded into managed memory. When ignore_checksum_failure is set to on and a checksum verify failure occurs, Greenplum Database generates a warning, and allows the page to be read into managed memory. If the page is then updated it is saved to disk and replicated to the mirror. If the page header is corrupt an error is reported even if this option is enabled.

Warning: Setting ignore_checksum_failure to on may propagate or hide data corruption or lead to other serious problems. However, if a checksum failure has already been detected and the page header is uncorrupted, setting ignore_checksum_failure to on may allow you to bypass the error and recover undamaged tuples that may still be present in the table.

The default setting is off, and it can only be changed by a superuser.

integer_datetimes

Reports whether PostgreSQL was built with support for 64-bit-integer dates and times.

IntervalStyle

Sets the display format for interval values. The value sql_standard produces output matching SQL standard interval literals. The value postgres produces output matching PostgreSQL releases prior to 8.4 when the DateStyle parameter was set to ISO.

The value postgres_verbose produces output matching Greenplum releases prior to 3.3 when the DateStyle parameter was set to non-ISO output.

The value iso_8601 will produce output matching the time interval format with designators defined in section 4.4.3.2 of ISO 8601. See the PostgreSQL 8.4 documentation for more information.

join_collapse_limit

The legacy query optimizer (planner) will rewrite explicit inner JOIN constructs into lists of FROM items whenever a list of no more than this many items in total would result. By default, this variable is set the same as from_collapse_limit, which is appropriate for most uses. Setting it to 1 prevents any reordering of inner JOINs. Setting this variable to a value between 1 and from_collapse_limit might be useful to trade off planning time against the quality of the chosen plan (higher values produce better plans).

keep_wal_segments

For Greenplum Database master mirroring, sets the maximum number of processed WAL segment files that are saved by the by the active Greenplum Database master if a checkpoint operation occurs.

The segment files are used to sycnronize the active master on the standby master.

krb_caseins_users

Sets whether Kerberos user names should be treated case-insensitively. The default is case sensitive (off).

krb_server_keyfile

Sets the location of the Kerberos server key file.

krb_srvname

Sets the Kerberos service name.

lc_collate

Reports the locale in which sorting of textual data is done. The value is determined when the Greenplum Database array is initialized.

lc_ctype

Reports the locale that determines character classifications. The value is determined when the Greenplum Database array is initialized.

lc_messages

Sets the language in which messages are displayed. The locales available depends on what was installed with your operating system - use locale -a to list available locales. The default value is inherited from the execution environment of the server. On some systems, this locale category does not exist. Setting this variable will still work, but there will be no effect. Also, there is a chance that no translated messages for the desired language exist. In that case you will continue to see the English messages.

lc_monetary

Sets the locale to use for formatting monetary amounts, for example with the to_char family of functions. The locales available depends on what was installed with your operating system - use locale -a to list available locales. The default value is inherited from the execution environment of the server.

lc_numeric

Sets the locale to use for formatting numbers, for example with the to_char family of functions. The locales available depends on what was installed with your operating system - use locale -a to list available locales. The default value is inherited from the execution environment of the server.

lc_time

This parameter currently does nothing, but may in the future.

listen_addresses

Specifies the TCP/IP address(es) on which the server is to listen for connections from client applications - a comma-separated list of host names and/or numeric IP addresses. The special entry * corresponds to all available IP interfaces. If the list is empty, only UNIX-domain sockets can connect.

local_preload_libraries

Comma separated list of shared library files to preload at the start of a client session.

log_autostats

Logs information about automatic ANALYZE operations related to gp_autostats_modeand gp_autostats_on_change_threshold.

log_connections

This outputs a line to the server log detailing each successful connection. Some client programs, like psql, attempt to connect twice while determining if a password is required, so duplicate “connection received” messages do not always indicate a problem.

log_disconnections

This outputs a line in the server log at termination of a client session, and includes the duration of the session.

log_dispatch_stats

When set to “on,” this parameter adds a log message with verbose information about the dispatch of the statement.

log_duration

Causes the duration of every completed statement which satisfies log_statement to be logged.

log_error_verbosity

Controls the amount of detail written in the server log for each message that is logged.

log_executor_stats

For each query, write performance statistics of the query executor to the server log. This is a crude profiling instrument. Cannot be enabled together with log_statement_stats.

log_hostname

By default, connection log messages only show the IP address of the connecting host. Turning on this option causes logging of the IP address and host name of the Greenplum Database master. Note that depending on your host name resolution setup this might impose a non-negligible performance penalty.

log_min_duration_statement

Logs the statement and its duration on a single log line if its duration is greater than or equal to the specified number of milliseconds. Setting this to 0 will print all statements and their durations. -1 deactivates the feature. For example, if you set it to 250 then all SQL statements that run 250ms or longer will be logged. Enabling this option can be useful in tracking down unoptimized queries in your applications.

log_min_error_statement

Controls whether or not the SQL statement that causes an error condition will also be recorded in the server log. All SQL statements that cause an error of the specified level or higher are logged. The default is ERROR. To effectively turn off logging of failing statements, set this parameter to PANIC.

log_min_messages

Controls which message levels are written to the server log. Each level includes all the levels that follow it. The later the level, the fewer messages are sent to the log.

If the Greenplum Database PL/Container extension is installed. This parameter also controls the PL/Container log level. For information about the extension, see PL/Container Language.

log_parser_stats

For each query, write performance statistics of the query parser to the server log. This is a crude profiling instrument. Cannot be enabled together with log_statement_stats.

log_planner_stats

For each query, write performance statistics of the legacy query optimizer (planner) to the server log. This is a crude profiling instrument. Cannot be enabled together with log_statement_stats.

log_rotation_age

Determines the maximum lifetime of an individual log file. After this time has elapsed, a new log file will be created. Set to zero to deactivate time-based creation of new log files.

log_rotation_size

Determines the maximum size of an individual log file. After this many kilobytes have been emitted into a log file, a new log file will be created. Set to zero to deactivate size-based creation of new log files.

The maximum value is INT_MAX/1024. If an invalid value is specified, the default value is used. INT_MAX is the largest value that can be stored as an integer on your system.

log_statement

Controls which SQL statements are logged. DDL logs all data definition commands like CREATE, ALTER, and DROP commands. MOD logs all DDL statements, plus INSERT, UPDATE, DELETE, TRUNCATE, and COPY FROM. PREPARE and EXPLAIN ANALYZE statements are also logged if their contained command is of an appropriate type.

log_statement_stats

For each query, write total performance statistics of the query parser, planner, and executor to the server log. This is a crude profiling instrument.

log_temp_files

Controls logging of temporary file names and sizes. Temporary files can be created for sorts, hashes, temporary query results and spill files. A log entry is made in pg_log for each temporary file when it is deleted. Depending on the source of the temporary files, the log entry could be created on either the master and/or segments. A log_temp_files value of zero logs all temporary file information, while positive values log only files whose size is greater than or equal to the specified number of kilobytes. The default setting is -1, which deactivates logging. Only superusers can change this setting.

log_timezone

Sets the time zone used for timestamps written in the log. Unlike TimeZone, this value is system-wide, so that all sessions will report timestamps consistently. The default is unknown, which means to use whatever the system environment specifies as the time zone.

log_truncate_on_rotation

Truncates (overwrites), rather than appends to, any existing log file of the same name. Truncation will occur only when a new file is being opened due to time-based rotation. For example, using this setting in combination with a log_filename such as gpseg#-%H.log would result in generating twenty-four hourly log files and then cyclically overwriting them. When off, pre-existing files will be appended to in all cases.

max_appendonly_tables

Sets the maximum number of concurrent transactions that can write to or update append-optimized tables. Transactions that exceed the maximum return an error.

Operations that are counted are INSERT, UPDATE, COPY, and VACUUM operations. The limit is only for in-progress transactions. Once a transaction ends (either aborted or committed), it is no longer counted against this limit.

For operations against a partitioned table, each subpartition (child table) that is an append-optimized table and is changed counts as a single table towards the maximum. For example, a partitioned table p_tbl is defined with three subpartitions that are append-optimized tables p_tbl_ao1, p_tbl_ao2, and p_tbl_ao3. An INSERT or UPDATE command against the partitioned table p_tbl that changes append-optimized tables p_tbl_ao1 and p_tbl_ao2 is counted as two transactions.

Increasing the limit allocates more shared memory on the master host at server start.

max_connections

The maximum number of concurrent connections to the database server. In a Greenplum Database system, user client connections go through the Greenplum master instance only. Segment instances should allow 5-10 times the amount as the master. When you increase this parameter, max_prepared_transactions must be increased as well. For more information about limiting concurrent connections, see “Configuring Client Authentication” in the Greenplum Database Administrator Guide.

Increasing this parameter might cause Greenplum Database to request more shared memory. See shared_buffers for information about Greenplum server instance shared memory buffers. If this value is increased, shared_buffers and the kernel parameter SHMMAX might also need to be increased. Also, parameters that depend on shared memory such as max_fsm_pages might need to be changed.

max_files_per_process

Sets the maximum number of simultaneously open files allowed to each server subprocess. If the kernel is enforcing a safe per-process limit, you don’t need to worry about this setting. Some platforms such as BSD, the kernel will allow individual processes to open many more files than the system can really support.

max_fsm_pages

Sets the maximum number of disk pages for which free space will be tracked in the shared free-space map. Six bytes of shared memory are consumed for each page slot. If this value is increased, shared_buffers and the kernel parameter SHMMAX might also need to be increased. Also, parameters that depend on shared memory such as max_connections might need to be changed.

max_fsm_relations

Sets the maximum number of relations for which free space will be tracked in the shared memory free-space map. Should be set to a value larger than the total number of:

tables + indexes + system tables

It costs about 60 bytes of memory for each relation per segment instance. It is better to allow some room for overhead and set too high rather than too low.

max_function_args

Reports the maximum number of function arguments.

max_identifier_length

Reports the maximum identifier length.

max_index_keys

Reports the maximum number of index keys.

max_locks_per_transaction

The shared lock table is created with room to describe locks on max_locks_per_transaction * (max_connections + max_prepared_transactions) objects, so no more than this many distinct objects can be locked at any one time. This is not a hard limit on the number of locks taken by any one transaction, but rather a maximum average value. You might need to raise this value if you have clients that touch many different tables in a single transaction.

max_prepared_transactions

Sets the maximum number of transactions that can be in the prepared state simultaneously. Greenplum uses prepared transactions internally to ensure data integrity across the segments. This value must be at least as large as the value of max_connections on the master. Segment instances should be set to the same value as the master.

max_resource_portals_per_transaction

Note: The max_resource_portals_per_transaction server configuration parameter is enforced only when resource queue-based resource management is active.

Sets the maximum number of simultaneously open user-declared cursors allowed per transaction. Note that an open cursor will hold an active query slot in a resource queue. Used for resource management.

max_resource_queues

Note: The max_resource_queues server configuration parameter is enforced only when resource queue-based resource management is active.

Sets the maximum number of resource queues that can be created in a Greenplum Database system. Note that resource queues are system-wide (as are roles) so they apply to all databases in the system.

max_stack_depth

Specifies the maximum safe depth of the server’s execution stack. The ideal setting for this parameter is the actual stack size limit enforced by the kernel (as set by ulimit -s or local equivalent), less a safety margin of a megabyte or so. Setting the parameter higher than the actual kernel limit will mean that a runaway recursive function can crash an individual backend process.

max_statement_mem

Sets the maximum memory limit for a query. Helps avoid out-of-memory errors on a segment host during query processing as a result of setting statement_mem too high.

Taking into account the configuration of a single segment host, calculate max_statement_mem as follows:

(seghost_physical_memory) / (average_number_concurrent_queries)

When changing both max_statement_mem and statement_mem, max_statement_mem must be changed first, or listed first in the postgresql.conf file.

memory_spill_ratio

Note: The memory_spill_ratio server configuration parameter is enforced only when resource group-based resource management is active.

Sets the memory usage threshold percentage for memory-intensive operators in a transaction. When a transaction reaches this threshold, it spills to disk.

The default memory_spill_ratio percentage is the value defined for the resource group assigned to the currently active role. You can set memory_spill_ratio at the session level to selectively set this limit on a per-query basis. For example, if you have a specific query that spills to disk and requires more memory, you may choose to set a larger memory_spill_ratio to increase the initial memory allocation.

When you set memory_spill_ratio at the session level, Greenplum Database does not perform semantic validation on the new value until you next perform a query.

You can specify an integer percentage value from 0 to 100 inclusive. If you specify a value of 0, Greenplum Database uses the statement_mem server configuration parameter value to control the initial query operator memory amount.

optimizer

Activates or deactivates GPORCA when running SQL queries. The default is on. If you deactivate GPORCA, Greenplum Database uses only the legacy query optimizer.

GPORCA co-exists with the legacy query optimizer. With GPORCA enabled, Greenplum Database uses GPORCA to generate an execution plan for a query when possible. If GPORCA cannot be used, then the legacy query optimizer is used.

The optimizer parameter can be set for a database system, an individual database, or a session or query.

For information about the legacy query optimizer and GPORCA, see Querying Datain the Greenplum Database Administrator Guide.

optimizer_analyze_root_partition

For a partitioned table, controls whether the ROOTPARTITION keyword is required to collect root partition statistics when the ANALYZE command is run on the table. GPORCA uses the root partition statistics when generating a query plan. The legacy query optimizer does not use these statistics.

The default setting for the parameter is on, the ANALYZE command can collect root partition statistics without the ROOTPARTITION keyword. Root partition statistics are collected when you run ANALYZE on the root partition, or when you run ANALYZE on a child leaf partition of the partitioned table and the other child leaf partitions have statistics. When the value is off, you must run ANALZYE ROOTPARTITION to collect root partition statistics.

When the value of the server configuration parameter optimizer is on (the default), the value of this parameter should also be on. For information about collecting table statistics on partitioned tables, see ANALYZE.

For information about the legacy query optimizer and GPORCA, see Querying Datain the Greenplum Database Administrator Guide.

optimizer_array_expansion_threshold

When GPORCA is enabled (the default) and is processing a query that contains a predicate with a constant array, the optimizer_array_expansion_threshold parameter limits the optimization process based on the number of constants in the array. If the array in the query predicate contains more than the number elements specified by parameter, GPORCA deactivates the transformation of the predicate into its disjunctive normal form during query optimization.

The default value is 100.

For example, when GPORCA is executing a query that contains an IN clause with more than 100 elements, GPORCA does not transform the predicate into its disjunctive normal form during query optimization to reduce optimization time consume less memory. The difference in query processing can be seen in the filter condition for the IN clause of the query EXPLAIN plan.

Changing the value of this parameter changes the trade-off between a shorter optimization time and lower memory consumption, and the potential benefits from constraint derivation during query optimization, for example conflict detection and partition elimination.

The parameter can be set for a database system, an individual database, or a session or query.

optimizer_control

Controls whether the server configuration parameter optimizer can be changed with SET, the RESET command, or the Greenplum Database utility gpconfig. If the optimizer_control parameter value is on, users can set the optimizer parameter. If the optimizer_control parameter value is off, the optimizer parameter cannot be changed.

optimizer_cost_model

When GPORCA is enabled (the default), this parameter controls the cost model that GPORCA chooses for bitmap scans used with bitmap indexes or with btree indexes on AO tables.

The experimental cost model is more likely to choose a faster bitmap index with nested loop joins instead of hash joins.

optimizer_cte_inlining_bound

When GPORCA is enabled (the default), this parameter controls the amount of inlining performed for common table expression (CTE) queries (queries that contain a WHERE clause). The default value, 0, deactivates inlining.

The parameter can be set for a database system, an individual database, or a session or query.

optimizer_dpe_stats

When GPORCA is enabled (the default) and this parameter is true (the default), GPORCA derives statistics that allow it to more accurately estimate the number of rows to be scanned during dynamic partition elimination.

The parameter can be set for a database system, an individual database, or a session or query.

optimizer_enable_associativity

When GPORCA is enabled (the default), this parameter controls whether the join associativity transform is enabled during query optimization. The transform analyzes join orders. For the default value off, only the GPORCA dynamic programming algorithm for analyzing join orders is enabled. The join associativity transform largely duplicates the functionality of the newer dynamic programming algorithm.

If the value is on, GPORCA can use the associativity transform during query optimization.

The parameter can be set for a database system, an individual database, or a session or query.

For information about GPORCA, see About GPORCAin the Greenplum Database Administrator Guide.

optimizer_enable_dml

When GPORCA is enabled (the default) and this parameter is true (the default), GPORCA attempts to execute DML commands such as INSERT, UPDATE, and DELETE. If GPORCA cannot execute the command, Greenplum Database falls back to the Postgres Planner.

When set to false, Greenplum Database always falls back to the Postgres Planner when performing DML commands.

The parameter can be set for a database system, an individual database, or a session or query.

For information about GPORCA, see About GPORCAin the Greenplum Database Administrator Guide.

optimizer_enable_master_only_queries

When GPORCA is enabled (the default), this parameter allows GPORCA to execute catalog queries that run only on the Greenplum Database master. For the default value off, only the Postgres Planner can execute catalog queries that run only on the Greenplum Database master.

The parameter can be set for a database system, an individual database, or a session or query.

Note: Enabling this parameter decreases performance of short running catalog queries. To avoid this issue, set this parameter only for a session or a query.

For information about GPORCA, see About GPORCAin the Greenplum Database Administrator Guide.

optimizer_force_agg_skew_avoidance

When GPORCA is enabled (the default), this parameter affects the query plan alternatives that GPORCA considers when 3 stage aggregate plans are generated. When the value is true, the default, GPORCA considers only 3 stage aggregate plans where the intermediate aggregation uses the GROUP BY and DISTINCT columns for distribution to reduce the effects of processing skew.

If the value is false, GPORCA can also consider a plan that uses GROUP BY columns for distribution. These plans might perform poorly when processing skew is present.

For information about GPORCA, see About GPORCAin the Greenplum Database Administrator Guide.

optimizer_force_multistage_agg

For the default settings, GPORCA is enabled and this parameter is true, GPORCA chooses a 3 stage aggregate plan for scalar distinct qualified aggregate when such a plan alternative is generated. When the value is false, GPORCA makes a cost based choice rather than a heuristic choice.

The parameter can be set for a database system, an individual database, or a session or query.

optimizer_force_three_stage_scalar_dqa

For the default settings, GPORCA is enabled and this parameter is true, GPORCA chooses a plan with multistage aggregates when such a plan alternative is generated. When the value is false, GPORCA makes a cost based choice rather than a heuristic choice.

The parameter can be set for a database system, an individual database, or a session, or query.

optimizer_join_arity_for_associativity_commutativity

The value is an optimization hint to limit the number of join associativity and join commutativity transformations explored during query optimization. The limit controls the alternative plans that GPORCA considers during query optimization. For example, the default value of 18 is an optimization hint for GPORCA to stop exploring join associativity and join commutativity transformations when an n-ary join operator has more than 18 children during optimization.

For a query with a large number of joins, specifying a lower value improves query performance by limiting the number of alternate query plans that GPORCA evaluates. However, setting the value too low might cause GPORCA to generate a query plan that performs sub-optimally.

This parameter has no effect when the optimizer_join_order parameter is set to query or greedy.

This parameter can be set for a database system or a session.

optimizer_join_order

When GPORCA is enabled, this parameter sets the optimization level for join ordering during query optimization by specifying which types of join ordering alternatives to evaluate.

• query - Uses the join order specified in the query.
• greedy - Evaluates the join order specified in the query and alternatives based on minimum cardinalities of the relations in the joins.
• exhaustive - Applies transformation rules to find and evaluate all join ordering alternatives.

The default value is exhaustive. Setting this parameter to query or greedy can generate a suboptimal query plan. However, if the administrator is confident that a satisfactory plan is generated with the query or greedy setting, query optimization time can be improved by setting the parameter to the lower optimization level.

Setting this parameter to query or greedy overrides the optimizer_join_order_threshold and optimizer_join_arity_for_associativity_commutativity parameters.

This parameter can be set for an individual database, a session, or a query.

optimizer_join_order_threshold

When GPORCA is enabled (the default), this parameter sets the maximum number of join children for which GPORCA will use the dynamic programming-based join ordering algorithm. You can set this value for a single query or for an entire session.

This parameter has no effect when the optimizer_join_query parameter is set to query or greedy.

optimizer_mdcache_size

Sets the maximum amount of memory on the Greenplum Database master that GPORCA uses to cache query metadata (optimization data) during query optimization. The memory limit session based. GPORCA caches query metadata during query optimization with the default settings: GPORCA is enabled and optimizer_metadata_caching is on.

The default value is 16384 (16MB). This is an optimal value that has been determined through performance analysis.

You can specify a value in KB, MB, or GB. The default unit is KB. For example, a value of 16384 is 16384KB. A value of 1GB is the same as 1024MB or 1048576KB. If the value is 0, the size of the cache is not limited.

This parameter can be set for a database system, an individual database, or a session or query.

optimizer_metadata_caching

When GPORCA is enabled (the default), this parameter specifies whether GPORCA caches query metadata (optimization data) in memory on the Greenplum Database master during query optimization. The default for this parameter is on, enable caching. The cache is session based. When a session ends, the cache is released. If the amount of query metadata exceeds the cache size, then old, unused metadata is evicted from the cache.

If the value is off, GPORCA does not cache metadata during query optimization.

This parameter can be set for a database system, an individual database, or a session or query.

The server configuration parameter optimizer_mdcache_size controls the size of the query metadata cache.

optimizer_minidump

GPORCA generates minidump files to describe the optimization context for a given query. The information in the file is not in a format that can be easily used for debugging or troubleshooting. The minidump file is located under the master data directory and uses the following naming format:

Minidump_date_time.mdp

The minidump file contains this query related information:

• Catalog objects including data types, tables, operators, and statistics required by GPORCA
• An internal representation (DXL) of the query
• An internal representation (DXL) of the plan produced by GPORCA
• System configuration information passed to GPORCA such as server configuration parameters, cost and statistics configuration, and number of segments
• A stack trace of errors generated while optimizing the query

Setting this parameter to ALWAYS generates a minidump for all queries. Set this parameter to ONERROR to minimize total optimization time.

For information about GPORCA, see About GPORCAin the Greenplum Database Administrator Guide.

optimizer_nestloop_factor

This parameter adds a costing factor to GPORCA to prioritize hash joins instead of nested loop joins during query optimization. The default value of 1024 was chosen after evaluating numerous workloads with uniformly distributed data. 1024 should be treated as the practical upper bound setting for this parameter. If you find the GPORCA selects hash joins more often than it should, reduce the value to shift the costing factor in favor of nested loop joins.

The parameter can be set for a database system, an individual database, or a session or query.

optimizer_parallel_union

When GPORCA is enabled (the default), optimizer_parallel_union controls the amount of parallelization that occurs for queries that contain a UNION or UNION ALL clause.

When the value is off, the default, GPORCA generates a query plan where each child of an APPEND(UNION) operator is in the same slice as the APPEND operator. During query execution, the children are executed in a sequential manner.

When the value is on, GPORCA generates a query plan where a redistribution motion node is under an APPEND(UNION) operator. During query execution, the children and the parent APPEND operator are on different slices, allowing the children of the APPEND(UNION) operator to execute in parallel on segment instances.

The parameter can be set for a database system, an individual database, or a session or query.

optimizer_penalize_skew

When GPORCA is enabled (the default), this parameter allows GPORCA to penalize the local cost of a HashJoin with a skewed Redistribute Motion as child to favor a Broadcast Motion during query optimization. The default value is true.

GPORCA determines there is skew for a Redistribute Motion when the NDV (number of distinct values) is less than the number of segments.

The parameter can be set for a database system, an individual database, or a session or query.

For information about GPORCA, see About GPORCAin the Greenplum Database Administrator Guide.

optimizer_print_missing_stats

When GPORCA is enabled (the default), this parameter controls the display of table column information about columns with missing statistics for a query. The default value is true, display the column information to the client. When the value is false, the information is not sent to the client.

The information is displayed during query execution, or with the EXPLAIN or EXPLAIN ANALYZE commands.

The parameter can be set for a database system, an individual database, or a session.

optimizer_print_optimization_stats

When GPORCA is enabled (the default), this parameter enables logging of GPORCA query optimization statistics for various optimization stages for a query. The default value is off, do not log optimization statistics. To log the optimization statistics, this parameter must be set to on and the parameter client_min_messages must be set to log.

• set optimizer_print_optimization_stats = on;
• set client_min_messages = 'log';

The information is logged during query execution, or with the EXPLAIN or EXPLAIN ANALYZE commands.

This parameter can be set for a database system, an individual database,or a session or query.

optimizer_sort_factor

When GPORCA is enabled (the default), optimizer_sort_factor controls the cost factor to apply to sorting operations during query optimization. The default value 1 specifies the default sort cost factor. The value is a ratio of increase or decrease from the default factor. For example, a value of 2.0 sets the cost factor at twice the default, and a value of 0.5 sets the factor at half the default.

The parameter can be set for a database system, an individual database, or a session or query.

optimizer_use_gpdb_allocators

When GPORCA is enabled (the default) and this parameter is true, GPORCA uses Greenplum Database memory management when executing queries. The default is false, GPORCA uses GPORCA-specific memory management. Greenplum Database memory management allows for faster optimization, reduced memory usage during optimization, and improves GPORCA support of vmem limits when compared to GPORCA-specific memory management.

For information about GPORCA, see About GPORCAin the Greenplum Database Administrator Guide.

optimizer_xform_bind_threshold

When GPORCA is enabled (the default), this parameter controls the maximum number of bindings per transform that GPORCA produces per group expression. Setting this parameter limits the number of alternatives that GPORCA creates, in many cases reducing the optimization time and overall memory usage of queries that include deeply nested expressions.

The default value is 0, GPORCA produces an unlimited set of bindings.

password_encryption

When a password is specified in CREATE USER or ALTER USER without writing either ENCRYPTED or UNENCRYPTED, this option determines whether the password is to be encrypted.

password_hash_algorithm

Specifies the cryptographic hash algorithm that is used when storing an encrypted Greenplum Database user password. The default algorithm is MD5.

For information about setting the password hash algorithm to protect user passwords, see “Protecting Passwords in Greenplum Database” in the Greenplum Database Administrator Guide.

pgcrypto.fips

Enables Greenplum Database support for a limited set of FIPS encryption functionality (Federal Information Processing Standard (FIPS) 140-2). For information about FIPS, see https://www.nist.gov/itl/popular-links/federal-information-processing-standards-fips. The default is off, encryption is not enabled.

Before enabling this parameter, ensure that FIPS is enabled on the Greenplum Database system hosts.

When this parameter is enabled, these changes occur:

• FIPS mode is initialized in the OpenSSL library
• The functions digest() and hmac() allow only the SHA encryption algorithm (MD5 is not allowed)
• The functions for the crypt and gen_salt algorithms are deactivated
• PGP encryption and decryption functions support only AES and 3DES encryption algorithms (other algorithms such as blowfish are not allowed)
• RAW encryption and decryption functions support only AES and 3DES (other algorithms such as blowfish are not allowed)

To enable pgcrypto.fips

1. Enable the pgcrypto functions as an extension if it is not enabled. See pgcrypto Cryptographic Functions.This example psql command creates the pgcrypto extension in the database testdb.

   psql -d testdb -c 'CREATE EXTENSION pgcrypto'

2. Configure the Greenplum Database server configuration parameter shared_preload_libraries to load the pgrcypto library. This example uses the gpconfig utility to update the parameter in the Greenplum Database postgresql.conf files.

   gpconfig -c shared_preload_libraries -v '\$libdir/pgcrypto'

   This command displays the value of shared_preload_libraries.

   gpconfig -s shared_preload_libraries

3. Restart the Greenplum Database system.

   gpstop -ra

4. Set the pgcrypto.fips server configuration parameter to on for each database that uses FIPS encryption. For example, this command sets the parameter to on for the database testdb.

   ALTER DATABASE testdb SET pgcrypto.fips TO on;

   Important: You must use the ALTER DATABASE command to set the parameter. You cannot use the SET command that updates the parameter for a session, or use the gpconfig utility that updates postgresql.conf files.

5. After setting the parameter, reconnect to the database to enable encryption support for a session. This example uses the psql meta command \c to connect to the testdb database.

   \c testdb

To deactivate pgcrypto.fips

1. If the database does not use pgcrypto functions, deactivate the pgcrypto extension. See pgcrypto Cryptographic Functions.This example psql command drops the pgcrypto extension in the database testdb.

   psql -d testdb -c 'DROP EXTENSION pgcrypto'

2. Remove \$libdir/pgcrypto from the shared_preload_libraries parameter, and restart Greenplum Database. This gpconfig command displays the value of the parameter from the Greenplum Database postgresql.conf files.

   gpconfig -s shared_preload_libraries

   Use the gpconfig utility with the -c and -v options to change the value of the parameter. Use the -r option to remove the parameter.

3. Restart the Greenplum Database system.

   gpstop -ra

pgstat_track_activity_query_size

Sets the maximum length limit for the query text stored in current_query column of the system catalog view pg_stat_activity. The minimum length is 1024 characters.

pljava_classpath

A colon (:) separated list of jar files or directories containing jar files needed for PL/Java functions. The full path to the jar file or directory must be specified, except the path can be omitted for jar files in the $GPHOME/lib/postgresql/java directory. The jar files must be installed in the same locations on all Greenplum hosts and readable by the gpadmin user.

The pljava_classpath parameter is used to assemble the PL/Java classpath at the beginning of each user session. Jar files added after a session has started are not available to that session.

If the full path to a jar file is specified in pljava_classpath it is added to the PL/Java classpath. When a directory is specified, any jar files the directory contains are added to the PL/Java classpath. The search does not descend into subdirectories of the specified directories. If the name of a jar file is included in pljava_classpath with no path, the jar file must be in the $GPHOME/lib/postgresql/java directory.

Note: Performance can be affected if there are many directories to search or a large number of jar files.

If pljava_classpath_insecure is false, setting the pljava_classpath parameter requires superuser privilege. Setting the classpath in SQL code will fail when the code is executed by a user without superuser privilege. The pljava_classpath parameter must have been set previously by a superuser or in the postgresql.conf file. Changing the classpath in the postgresql.conf file requires a reload (gpstop -u).

pljava_classpath_insecure

Controls whether the server configuration parameter pljava_classpath can be set by a user without Greenplum Database superuser privileges. When true, pljava_classpath can be set by a regular user. Otherwise, pljava_classpath can be set only by a database superuser. The default is false.

Warning: Enabling this parameter exposes a security risk by giving non-administrator database users the ability to run unauthorized Java methods.

pljava_statement_cache_size

Sets the size in KB of the JRE MRU (Most Recently Used) cache for prepared statements.

pljava_release_lingering_savepoints

If true, lingering savepoints used in PL/Java functions will be released on function exit. If false, savepoints will be rolled back.

pljava_vmoptions

Defines the startup options for the Java VM. The default value is an empty string (“”).

port

The database listener port for a Greenplum instance. The master and each segment has its own port. Port numbers for the Greenplum system must also be changed in the gp_segment_configuration catalog. You must shut down your Greenplum Database system before changing port numbers.

random_page_cost

Sets the estimate of the cost of a nonsequentially fetched disk page for the legacy query optimizer (planner). This is measured as a multiple of the cost of a sequential page fetch. A higher value makes it more likely a sequential scan will be used, a lower value makes it more likely an index scan will be used.

readable_external_table_timeout

When an SQL query reads from an external table, the parameter value specifies the amount of time in seconds that Greenplum Database waits before cancelling the query when data stops being returned from the external table.

The default value of 0, specifies no time out. Greenplum Database does not cancel the query.

If queries that use gpfdist run a long time and then return the error “intermittent network connectivity issues”, you can specify a value for readable_external_table_timeout. If no data is returned by gpfdist for the specified length of time, Greenplum Database cancels the query.

repl_catchup_within_range

For Greenplum Database master mirroring, controls updates to the active master. If the number of WAL segment files that have not been processed by the walsender exceeds this value, Greenplum Database updates the active master.

If the number of segment files does not exceed the value, Greenplum Database blocks updates to the to allow the walsender process the files. If all WAL segments have been processed, the active master is updated.

replication_timeout

For Greenplum Database master mirroring, sets the maximum time in milliseconds that the walsender process on the active master waits for a status message from the walreceiver process on the standby master. If a message is not received, the walsender logs an error message.

The wal_receiver_status_interval controls the interval between walreceiver status messages.

regex_flavor

The ‘extended’ setting may be useful for exact backwards compatibility with pre-7.4 releases of PostgreSQL.

resource_cleanup_gangs_on_wait

Note: The resource_cleanup_gangs_on_wait server configuration parameter is enforced only when resource queue-based resource management is active.

If a statement is submitted through a resource queue, clean up any idle query executor worker processes before taking a lock on the resource queue.

resource_select_only

Note: The resource_select_only server configuration parameter is enforced only when resource queue-based resource management is active.

Sets the types of queries managed by resource queues. If set to on, then SELECT, SELECT INTO, CREATE TABLE AS SELECT, and DECLARE CURSOR commands are evaluated. If set to off INSERT, UPDATE, and DELETE commands will be evaluated as well.

runaway_detector_activation_percent

For queries that are managed by resource queues or resource groups, this parameter determines when Greenplum Database terminates running queries based on the amount of memory the queries are using. A value of 100 deactivates the automatic termination of queries based on the percentage of memory that is utilized.

Either the resource queue or the resource group management scheme can be active in Greenplum Database; both schemes cannot be active at the same time. The server configuration parameter gp_resource_manager controls which scheme is active.

When resource queues are enabled - This parameter sets the percent of utilized Greenplum Database vmem memory that triggers the termination of queries. If the percentage of vmem memory that is utilized for a Greenplum Database segment exceeds the specified value, Greenplum Database terminates queries managed by resource queues based on memory usage, starting with the query consuming the largest amount of memory. Queries are terminated until the percentage of utilized vmem is below the specified percentage.

Specify the maximum vmem value for active Greenplum Database segment instances with the server configuration parameter gp_vmem_protect_limit.

For example, if vmem memory is set to 10GB, and this parameter is 90 (90%), Greenplum Database starts terminating queries when the utilized vmem memory exceeds 9 GB.

For information about resource queues, see Using Resource Queues.

When resource groups are enabled - This parameter sets the percent of utilized resource group global shared memory that triggers the termination of queries that are managed by resource groups that are configured to use the vmtracker memory auditor, such as admin_group and default_group. For information about memory auditors, see Memory Auditor.

Resource groups have a global shared memory pool when the sum of the MEMORY_LIMIT attribute values configured for all resource groups is less than 100. For example, if you have 3 resource groups configured with memory_limit values of 10 , 20, and 30, then global shared memory is 40% = 100% - (10% + 20% + 30%). See Global Shared Memory.

If the percentage of utilized global shared memory exceeds the specified value, Greenplum Database terminates queries based on memory usage, selecting from queries managed by the resource groups that are configured to use the vmtracker memory auditor. Greenplum Database starts with the query consuming the largest amount of memory. Queries are terminated until the percentage of utilized global shared memory is below the specified percentage.

For example, if global shared memory is 10GB, and this parameter is 90 (90%), Greenplum Database starts terminating queries when the utilized global shared memory exceeds 9 GB.

For information about resource groups, see Using Resource Groups.

search_path

Specifies the order in which schemas are searched when an object is referenced by a simple name with no schema component. When there are objects of identical names in different schemas, the one found first in the search path is used. The system catalog schema, pg_catalog, is always searched, whether it is mentioned in the path or not. When objects are created without specifying a particular target schema, they will be placed in the first schema listed in the search path. The current effective value of the search path can be examined via the SQL function current_schemas(). current_schemas() shows how the requests appearing in search_path were resolved.

seq_page_cost

For the legacy query optimizer (planner), sets the estimate of the cost of a disk page fetch that is part of a series of sequential fetches.

server_encoding

Reports the database encoding (character set). It is determined when the Greenplum Database array is initialized. Ordinarily, clients need only be concerned with the value of client_encoding.

server_version

Reports the version of PostgreSQL that this release of Greenplum Database is based on.

server_version_num

Reports the version of PostgreSQL that this release of Greenplum Database is based on as an integer.

shared_buffers

Sets the amount of memory a Greenplum Database segment instance uses for shared memory buffers. This setting must be at least 128KB and at least 16KB times max_connections.

Each Greenplum Database segment instance calculates and attempts to allocate certain amount of shared memory based on the segment configuration. The value of shared_buffers is significant portion of this shared memory calculation, but is not all it. When setting shared_buffers, the values for the operating system parameters SHMMAX or SHMALL might also need to be adjusted.

The operating system parameter SHMMAX specifies maximum size of a single shared memory allocation. The value of SHMMAX must be greater than this value:

 `shared_buffers` + <other_seg_shmem>

The value of other_seg_shmem is the portion the Greenplum Database shared memory calculation that is not accounted for by the shared_buffers value. The other_seg_shmem value will vary based on the segment configuration.

With the default Greenplum Database parameter values, the value for other_seg_shmem is approximately 111MB for Greenplum Database segments and approximately 79MB for the Greenplum Database master.

The operating system parameter SHMALL specifies the maximum amount of shared memory on the host. The value of SHMALL must be greater than this value:

 (<num_instances_per_host> * ( `shared_buffers` + <other_seg_shmem> )) + <other_app_shared_mem>

The value of other_app_shared_mem is the amount of shared memory that is used by other applications and processes on the host.

When shared memory allocation errors occur, possible ways to resolve shared memory allocation issues are to increase SHMMAX or SHMALL, or decrease shared_buffers or max_connections.

See the Greenplum Database Installation Guide for information about the Greenplum Database values for the parameters SHMMAX and SHMALL.

shared_preload_libraries

A comma-separated list of shared libraries that are to be preloaded at server start. PostgreSQL procedural language libraries can be preloaded in this way, typically by using the syntax ‘$libdir/plXXX‘ where XXX is pgsql, perl, tcl, or python. By preloading a shared library, the library startup time is avoided when the library is first used. If a specified library is not found, the server will fail to start.

Note: When you add a library to shared_preload_libraries, be sure to retain any previous setting of the parameter.

ssl

Enables SSL connections.

ssl_ciphers

Specifies a list of SSL ciphers that are allowed to be used on secure connections. See the openssl manual page for a list of supported ciphers.

standard_conforming_strings

Determines whether ordinary string literals (‘…’) treat backslashes literally, as specified in the SQL standard. The default value is on. Turn this parameter off to treat backslashes in string literals as escape characters instead of literal backslashes. Applications may check this parameter to determine how string literals are processed. The presence of this parameter can also be taken as an indication that the escape string syntax (E’…’) is supported.

statement_mem

Allocates segment host memory per query. The amount of memory allocated with this parameter cannot exceed max_statement_mem or the memory limit on the resource queue or resource group through which the query was submitted. If additional memory is required for a query, temporary spill files on disk are used.

If you are using resource groups to control resource allocation in your Greenplum Database cluster:

• Greenplum Database uses statement_mem to control query memory usage when the resource group MEMORY_SPILL_RATIO is set to 0.

• You can use the following calculation to estimate a reasonable statement_mem value:

  rg_perseg_mem = ((RAM * (vm.overcommit_ratio / 100) + SWAP) * gp_resource_group_memory_limit) / num_active_primary_segments_per_host
  statement_mem = rg_perseg_mem / max_expected_concurrent_queries

If you are using resource queues to control resource allocation in your Greenplum Database cluster:

• When gp_resqueue_memory_policy =auto, statement_mem and resource queue memory limits control query memory usage.

• You can use the following calculation to estimate a reasonable statement_mem value for a wide variety of situations:

  ( <gp_vmem_protect_limit>GB * .9 ) / <max_expected_concurrent_queries>

  For example, with a gp_vmem_protect_limit set to 8192MB (8GB) and assuming a maximum of 40 concurrent queries with a 10% buffer, you would use the following calculation to determine the statement_mem value:

  (8GB * .9) / 40 = .18GB = 184MB

When changing both max_statement_mem and statement_mem, max_statement_mem must be changed first, or listed first in the postgresql.conf file.

statement_timeout

Abort any statement that takes over the specified number of milliseconds. 0 turns off the limitation.

stats_queue_level

Note: The stats_queue_level server configuration parameter is enforced only when resource queue-based resource management is active.

Collects resource queue statistics on database activity.

superuser_reserved_connections

Determines the number of connection slots that are reserved for Greenplum Database superusers.

tcp_keepalives_count

How many keepalives may be lost before the connection is considered dead. A value of 0 uses the system default. If TCP_KEEPCNT is not supported, this parameter must be 0.

Use this parameter for all connections that are not between a primary and mirror segment. Use gp_filerep_tcp_keepalives_count for settings that are between a primary and mirror segment.

tcp_keepalives_idle

Number of seconds between sending keepalives on an otherwise idle connection. A value of 0 uses the system default. If TCP_KEEPIDLE is not supported, this parameter must be 0.

Use this parameter for all connections that are not between a primary and mirror segment. Use gp_filerep_tcp_keepalives_idle for settings that are between a primary and mirror segment.

tcp_keepalives_interval

How many seconds to wait for a response to a keepalive before retransmitting. A value of 0 uses the system default. If TCP_KEEPINTVL is not supported, this parameter must be 0.

Use this parameter for all connections that are not between a primary and mirror segment. Use gp_filerep_tcp_keepalives_interval for settings that are between a primary and mirror segment.

temp_buffers

Sets the maximum number of temporary buffers used by each database session. These are session-local buffers used only for access to temporary tables. The setting can be changed within individual sessions, but only up until the first use of temporary tables within a session. The cost of setting a large value in sessions that do not actually need a lot of temporary buffers is only a buffer descriptor, or about 64 bytes, per increment. However if a buffer is actually used, an additional 8192 bytes will be consumed.

TimeZone

Sets the time zone for displaying and interpreting time stamps. The default is to use whatever the system environment specifies as the time zone. See Date/Time Keywords in the PostgreSQL documentation.

timezone_abbreviations

Sets the collection of time zone abbreviations that will be accepted by the server for date time input. The default is Default, which is a collection that works in most of the world. Australia and India, and other collections can be defined for a particular installation. Possible values are names of configuration files stored in $GPHOME/share/postgresql/timezonesets/.

To configure Greenplum Database to use a custom collection of timezones, copy the file that contains the timezone definitions to the directory $GPHOME/share/postgresql/timezonesets/ on the Greenplum Database master and segment hosts. Then set value of the server configuration parameter timezone_abbreviations to the file. For example, to use a file custom that contains the default timezones and the WIB (Waktu Indonesia Barat) timezone.

1. Copy the file Default from the directory $GPHOME/share/postgresql/timezonesets/ the file custom. Add the WIB timezone information from the file Asia.txt to the custom.
2. Copy the file custom to the directory $GPHOME/share/postgresql/timezonesets/ on the Greenplum Database master and segment hosts.
3. Set value of the server configuration parameter timezone_abbreviations to custom.
4. Reload the server configuration file (gpstop -u).

track_activities

Enables the collection of information on the currently executing command of each session, along with the time when that command began execution. This parameter is true by default. Only superusers can change this setting. See the pg_stat_activity view.

Note: Even when enabled, this information is not visible to all users, only to superusers and the user owning the session being reported on, so it should not represent a security risk.

track_activity_query_size

Sets the maximum length limit for the query text stored in current_query column of the system catalog view pg_stat_activity. The minimum length is 1024 characters.

track_counts

Collects information about executing commands. Enables the collection of information on the currently executing command of each session, along with the time at which that command began execution.

transaction_isolation

Sets the current transaction’s isolation level.

transaction_read_only

Sets the current transaction’s read-only status.

transform_null_equals

When on, expressions of the form expr = NULL (or NULL = expr) are treated as expr IS NULL, that is, they return true if expr evaluates to the null value, and false otherwise. The correct SQL-spec-compliant behavior of expr = NULL is to always return null (unknown).

unix_socket_directory

Specifies the directory of the UNIX-domain socket on which the server is to listen for connections from client applications. The default is an empty string which is the directory /tmp/.

Important: Do not change the value of this parameter. The default location is required for Greenplum Database utilities.

unix_socket_group

Sets the owning group of the UNIX-domain socket. By default this is an empty string, which uses the default group for the current user.

unix_socket_permissions

Sets the access permissions of the UNIX-domain socket. UNIX-domain sockets use the usual UNIX file system permission set. Note that for a UNIX-domain socket, only write permission matters.

update_process_title

Enables updating of the process title every time a new SQL command is received by the server. The process title is typically viewed by the ps command.

vacuum_cost_delay

The length of time that the process will sleep when the cost limit has been exceeded. 0 deactivates the cost-based vacuum delay feature.

vacuum_cost_limit

The accumulated cost that will cause the vacuuming process to sleep.

vacuum_cost_page_dirty

The estimated cost charged when vacuum modifies a block that was previously clean. It represents the extra I/O required to flush the dirty block out to disk again.

vacuum_cost_page_hit

The estimated cost for vacuuming a buffer found in the shared buffer cache. It represents the cost to lock the buffer pool, lookup the shared hash table and scan the content of the page.

vacuum_cost_page_miss

The estimated cost for vacuuming a buffer that has to be read from disk. This represents the effort to lock the buffer pool, lookup the shared hash table, read the desired block in from the disk and scan its content.

vacuum_freeze_min_age

Specifies the cutoff age (in transactions) that VACUUM should use to decide whether to replace transaction IDs with FrozenXID while scanning a table.

For information about VACUUM and transaction ID management, see “Managing Data” in the Greenplum Database Administrator Guide and the PostgreSQL documentation.

validate_previous_free_tid

Enables a test that validates the free tuple ID (TID) list. The list is maintained and used by Greenplum Database. Greenplum Database determines the validity of the free TID list by ensuring the previous free TID of the current free tuple is a valid free tuple. The default value is true, enable the test.

If Greenplum Database detects a corruption in the free TID list, the free TID list is rebuilt, a warning is logged, and a warning is returned by queries for which the check failed. Greenplum Database attempts to execute the queries.

Note: If a warning is returned, please contact VMware Support.

verify_gpfdists_cert

When a Greenplum Database external table is defined with the gpfdists protocol to use SSL security, this parameter controls whether SSL certificate authentication is enabled. The default is true, SSL authentication is enabled when Greenplum Database communicates with the gpfdist utility to either read data from or write data to an external data source.

The value false deactivates SSL certificate authentication. These SSL exceptions are ignored:

• The self-signed SSL certificate that is used by gpfdist is not trusted by Greenplum Database.
• The host name contained in the SSL certificate does not match the host name that is running gpfdist.

You can set the value to false to deactivate authentication when testing the communication between the Greenplum Database external table and the gpfdist utility that is serving the external data.

Warning: Deactivating SSL certificate authentication exposes a security risk by not validating the gpfdists SSL certificate.

For information about the gpfdists protocol, see gpfdists:// Protocol. For information about running the gpfdist utility, see gpfdist.

vmem_process_interrupt

Enables checking for interrupts before reserving vmem memory for a query during Greenplum Database query execution. Before reserving further vmem for a query, check if the current session for the query has a pending query cancellation or other pending interrupts. This ensures more responsive interrupt processing, including query cancellation requests. The default is off.

wal_receiver_status_interval

For Greenplum Database master mirroring, sets the interval in seconds between walreceiver process status messages that are sent to the active master. Under heavy loads, the time might be longer.

The value of replication_timeout controls the time that the walsender process waits for a walreceiver message.

writable_external_table_bufsize

Size of the buffer (in KB) that Greenplum Database uses for network communication, such as the gpfdist utility and external web tables (that use http). Greenplum Database stores data in the buffer before writing the data out. For information about gpfdist, see the Greenplum Database Utility Guide.

xid_stop_limit

The number of transaction IDs prior to the ID where transaction ID wraparound occurs. When this limit is reached, Greenplum Database stops creating new transactions to avoid data loss due to transaction ID wraparound.

xid_warn_limit

The number of transaction IDs prior to the limit specified by xid_stop_limit. When Greenplum Database reaches this limit, it issues a warning to perform a VACUUM operation to avoid data loss due to transaction ID wraparound.

xmlbinary

Specifies how binary values are encoded in XML data. For example, when bytea values are converted to XML. The binary data can be converted to either base64 encoding or hexadecimal encoding. The default is base64.

The parameter can be set for a database system, an individual database, or a session.

xmloption

Specifies whether XML data is to be considered as an XML document (document) or XML content fragment (content) for operations that perform implicit parsing and serialization. The default is content.

This parameter affects the validation performed by xml_is_well_formed(). If the value is document, the function checks for a well-formed XML document. If the value is content, the function checks for a well-formed XML content fragment.

Note: An XML document that contains a document type declaration (DTD) is not considered a valid XML content fragment. If xmloption set to content, XML that contains a DTD is not considered valid XML.

To cast a character string that contains a DTD to the xml data type, use the xmlparse function with the document keyword, or change the xmloption value to document.

The parameter can be set for a database system, an individual database, or a session. The SQL command to set this option for a session is also available in Greenplum Database.

SET XML OPTION { DOCUMENT | CONTENT }