Information Schema

information_schema is a special schema that contains virtual tables which are read-only and can be queried to get information about the state of the cluster.

Table of Contents

• Access
• Virtual Tables
  • tables
    • settings
  • views
  • columns
  • table_constraints
  • key_column_usage
  • table_partitions
  • routines
  • schemata
  • sql_features
  • ingestion_rules

Access

When the user management is enabled, accessing the information_schema is open to all users and it does not require any privileges.

However, being able to query information_schema tables will not allow the user to retrieve all the rows in the table, as it can contain information related to tables over which the connected user does not have any privileges. The only rows that will be returned will be the ones the user is allowed to access.

For example, if the user john has any privilege on the doc.books table but no privilege at all on doc.locations, when john issues a SELECT * FROM information_schema.tables statement, the tables information related to the doc.locations table will not be returned.

Virtual Tables

tables

The information_schema.tables virtual table can be queried to get a list of all available tables and views and their settings, such as number of shards or number of replicas.

cr> SELECT table_schema, table_name, table_type, number_of_shards, number_of_replicas
... FROM information_schema.tables
... ORDER BY table_schema ASC, table_name ASC;
+--------------------+-------------------------+------------+------------------+--------------------+
| table_schema       | table_name              | table_type | number_of_shards | number_of_replicas |
+--------------------+-------------------------+------------+------------------+--------------------+
| doc                | galaxies                | VIEW       |             NULL | NULL               |
| doc                | locations               | BASE TABLE |                2 | 0                  |
| doc                | partitioned_table       | BASE TABLE |                4 | 0-1                |
| doc                | quotes                  | BASE TABLE |                2 | 0                  |
| information_schema | columns                 | BASE TABLE |             NULL | NULL               |
| information_schema | ingestion_rules         | BASE TABLE |             NULL | NULL               |
| information_schema | key_column_usage        | BASE TABLE |             NULL | NULL               |
| information_schema | referential_constraints | BASE TABLE |             NULL | NULL               |
| information_schema | routines                | BASE TABLE |             NULL | NULL               |
| information_schema | schemata                | BASE TABLE |             NULL | NULL               |
| information_schema | sql_features            | BASE TABLE |             NULL | NULL               |
| information_schema | table_constraints       | BASE TABLE |             NULL | NULL               |
| information_schema | table_partitions        | BASE TABLE |             NULL | NULL               |
| information_schema | tables                  | BASE TABLE |             NULL | NULL               |
| information_schema | views                   | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_attrdef              | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_attribute            | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_class                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_constraint           | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_database             | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_description          | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_index                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_namespace            | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_type                 | BASE TABLE |             NULL | NULL               |
| sys                | allocations             | BASE TABLE |             NULL | NULL               |
| sys                | checks                  | BASE TABLE |             NULL | NULL               |
| sys                | cluster                 | BASE TABLE |             NULL | NULL               |
| sys                | health                  | BASE TABLE |             NULL | NULL               |
| sys                | jobs                    | BASE TABLE |             NULL | NULL               |
| sys                | jobs_log                | BASE TABLE |             NULL | NULL               |
| sys                | jobs_metrics            | BASE TABLE |             NULL | NULL               |
| sys                | node_checks             | BASE TABLE |             NULL | NULL               |
| sys                | nodes                   | BASE TABLE |             NULL | NULL               |
| sys                | operations              | BASE TABLE |             NULL | NULL               |
| sys                | operations_log          | BASE TABLE |             NULL | NULL               |
| sys                | privileges              | BASE TABLE |             NULL | NULL               |
| sys                | repositories            | BASE TABLE |             NULL | NULL               |
| sys                | shards                  | BASE TABLE |             NULL | NULL               |
| sys                | snapshots               | BASE TABLE |             NULL | NULL               |
| sys                | summits                 | BASE TABLE |             NULL | NULL               |
| sys                | users                   | BASE TABLE |             NULL | NULL               |
+--------------------+-------------------------+------------+------------------+--------------------+
SELECT 41 rows in set (... sec)

The table also contains additional information such as specified routing (Sharding) and partitioned by (Partitioned Tables) columns:

cr> SELECT table_name, clustered_by, partitioned_by
... FROM information_schema.tables
... WHERE table_schema = 'doc'
... ORDER BY table_schema ASC, table_name ASC;
+-------------------+--------------+----------------+
| table_name        | clustered_by | partitioned_by |
+-------------------+--------------+----------------+
| galaxies          | NULL         | NULL           |
| locations         | id           | NULL           |
| partitioned_table | _id          | ["date"]       |
| quotes            | id           | NULL           |
+-------------------+--------------+----------------+
SELECT 4 rows in set (... sec)

Schema

settings

Table settings specify configuration parameters for tables. Some settings can be set during Cluster runtime and others are only applied on cluster restart.

This list of table settings in WITH shows detailed information of each parameter.

Table parameters can be applied with CREATE TABLE on creation of a table. With ALTER TABLE they can be set on already existing tables.

The following statement creates a new table and sets the refresh interval of shards to 500 ms and sets the shard allocation for primary shards only:

cr> create table parameterized_table (id int, content string)
... with ("refresh_interval"=500, "routing.allocation.enable"='primaries');
CREATE OK, 1 row affected (... sec)

The settings can be verified by querying information_schema.tables:

cr> select settings['routing']['allocation']['enable'] as alloc_enable,
...   settings['refresh_interval'] as refresh_interval
... from information_schema.tables
... where table_name='parameterized_table';
+--------------+------------------+
| alloc_enable | refresh_interval |
+--------------+------------------+
| primaries    |              500 |
+--------------+------------------+
SELECT 1 row in set (... sec)

On existing tables this needs to be done with ALTER TABLE statement:

cr> alter table parameterized_table
... set ("routing.allocation.enable"='none');
ALTER OK, -1 rows affected (... sec)

views

The table information_schema.views contains the name, definition and options of all available views.

cr> SELECT table_schema, table_name, view_definition
... FROM information_schema.views
... ORDER BY table_schema ASC, table_name ASC;
+--------------+------------+-------------------------+
| table_schema | table_name | view_definition         |
+--------------+------------+-------------------------+
| doc          | galaxies   | SELECT                  |
|              |            |   "id"                  |
|              |            | , "name"                |
|              |            | , "description"         |
|              |            | FROM "locations"        |
|              |            | WHERE "kind" = 'Galaxy' |
+--------------+------------+-------------------------+
SELECT 1 row in set (... sec)

Schema

Note

If you drop the table of a view, the view will still exist and show up in the information_schema.tables and information_schema.views tables.

columns

This table can be queried to get a list of all available columns of all tables and views and their definition like data type and ordinal position inside the table:

cr> select table_name, column_name, ordinal_position as pos, data_type
... from information_schema.columns
... where table_schema = 'doc' and table_name not like 'my_table%'
... order by table_name asc, column_name asc;
+-------------------+--------------------------------+------+--------------+
| table_name        | column_name                    |  pos | data_type    |
+-------------------+--------------------------------+------+--------------+
| locations         | date                           |    1 | timestamp    |
| locations         | description                    |    2 | string       |
| locations         | id                             |    3 | string       |
| locations         | information                    |    4 | object_array |
| locations         | information['evolution_level'] | NULL | short        |
| locations         | information['population']      | NULL | long         |
| locations         | kind                           |    5 | string       |
| locations         | name                           |    6 | string       |
| locations         | position                       |    7 | integer      |
| locations         | race                           |    8 | object       |
| locations         | race['description']            | NULL | string       |
| locations         | race['interests']              | NULL | string_array |
| locations         | race['name']                   | NULL | string       |
| partitioned_table | date                           |    1 | timestamp    |
| partitioned_table | id                             |    2 | long         |
| partitioned_table | title                          |    3 | string       |
| quotes            | id                             |    1 | integer      |
| quotes            | quote                          |    2 | string       |
+-------------------+--------------------------------+------+--------------+
SELECT 18 rows in set (... sec)

You can even query this tables’ own columns (attention: this might lead to infinite recursion of your mind, beware!):

cr> select column_name, data_type, ordinal_position
... from information_schema.columns
... where table_schema = 'information_schema'
... and table_name = 'columns' order by ordinal_position asc;
+---------------------------+-----------+------------------+
| column_name               | data_type | ordinal_position |
+---------------------------+-----------+------------------+
| character_maximum_length  | integer   |                1 |
| character_octet_length    | integer   |                2 |
| character_set_catalog     | string    |                3 |
| character_set_name        | string    |                4 |
| character_set_schema      | string    |                5 |
| check_action              | integer   |                6 |
| check_references          | string    |                7 |
| collation_catalog         | string    |                8 |
| collation_name            | string    |                9 |
| collation_schema          | string    |               10 |
| column_default            | string    |               11 |
| column_name               | string    |               12 |
| data_type                 | string    |               13 |
| datetime_precision        | integer   |               14 |
| domain_catalog            | string    |               15 |
| domain_name               | string    |               16 |
| domain_schema             | string    |               17 |
| generation_expression     | string    |               18 |
| interval_precision        | integer   |               19 |
| interval_type             | string    |               20 |
| is_generated              | boolean   |               21 |
| is_nullable               | boolean   |               22 |
| numeric_precision         | integer   |               23 |
| numeric_precision_radix   | integer   |               24 |
| numeric_scale             | integer   |               25 |
| ordinal_position          | short     |               26 |
| table_catalog             | string    |               27 |
| table_name                | string    |               28 |
| table_schema              | string    |               29 |
| user_defined_type_catalog | string    |               30 |
| user_defined_type_name    | string    |               31 |
| user_defined_type_schema  | string    |               32 |
+---------------------------+-----------+------------------+
SELECT 32 rows in set (... sec)

Note

Columns are always sorted alphabetically in ascending order regardless of the order they were defined on table creation. Thus the ordinal_position reflects the alphabetical position.

Schema

table_constraints

This table can be queried to get a list of all defined table constraints, their type, name and which table they are defined in.

Note

Currently only PRIMARY_KEY constraints are supported.

cr> select table_schema, table_name, constraint_name, constraint_type as type
... from information_schema.table_constraints
... where table_name = 'tables'
...   or table_name = 'quotes'
...   or table_name = 'documents'
...   or table_name = 'tbl'
... order by table_schema desc, table_name asc limit 10;
+--------------------+------------+-...------------------+-------------+
| table_schema       | table_name | constraint_name      | type        |
+--------------------+------------+-...------------------+-------------+
| information_schema | tables     | tables_pk            | PRIMARY KEY |
| doc                | quotes     | quotes_pk            | PRIMARY KEY |
| doc                | tbl        | doc_tbl_col_not_null | CHECK       |
+--------------------+------------+-...------------------+-------------+
SELECT 3 rows in set (... sec)

key_column_usage

This table may be queried to retrieve primary key information from all user tables:

cr> select constraint_name, table_name, column_name, ordinal_position
... from information_schema.key_column_usage
... where table_name = 'students'
+-----------------+------------+-------------+------------------+
| constraint_name | table_name | column_name | ordinal_position |
+-----------------+------------+-------------+------------------+
| students_pk     | students   | id          |                1 |
| students_pk     | students   | department  |                2 |
+-----------------+------------+-------------+------------------+
SELECT 2 rows in set (... sec)

Schema

table_partitions

This table can be queried to get information about all partitioned tables, Each partition of a table is represented as one row. The row contains the information table name, schema name, partition ident, and the values of the partition. values is a key-value object with the ‘partitioned by column’ as key(s) and the corresponding value as value(s).

For further information see Partitioned Tables.

cr> insert into a_partitioned_table (id, content) values (1, 'content_a');
INSERT OK, 1 row affected (... sec)

cr> alter table a_partitioned_table set (number_of_shards=5);
ALTER OK, -1 rows affected (... sec)

cr> insert into a_partitioned_table (id, content) values (2, 'content_b');
INSERT OK, 1 row affected (... sec)

The following example shows a table where the column ‘content’ of table ‘a_partitioned_table’ has been used to partition the table. The table has two partitions. The partitions are introduced when data is inserted where ‘content’ is ‘content_a’, and ‘content_b’.:

cr> select table_name, schema_name as schema, partition_ident, "values"
... from information_schema.table_partitions
... order by table_name, partition_ident;
+---------------------+--------+--------------------+--------------------------+
| table_name          | schema | partition_ident    | values                   |
+---------------------+--------+--------------------+--------------------------+
| a_partitioned_table | doc    | 04566rreehimst2vc4 | {"content": "content_a"} |
| a_partitioned_table | doc    | 04566rreehimst2vc8 | {"content": "content_b"} |
+---------------------+--------+--------------------+--------------------------+
SELECT 2 rows in set (... sec)

The second partition has been created after the number of shards for future partitions have been changed on the partitioned table, so they show 5 instead of 4:

cr> select table_name, partition_ident,
... number_of_shards, number_of_replicas
... from information_schema.table_partitions
... order by table_name, partition_ident;
+---------------------+--------------------+------------------+--------------------+
| table_name          | partition_ident    | number_of_shards | number_of_replicas |
+---------------------+--------------------+------------------+--------------------+
| a_partitioned_table | 04566rreehimst2vc4 |                4 | 0-1                |
| a_partitioned_table | 04566rreehimst2vc8 |                5 | 0-1                |
+---------------------+--------------------+------------------+--------------------+
SELECT 2 rows in set (... sec)

routines

The routines table contains tokenizers, token-filters, char-filters, custom analyzers created by CREATE ANALYZER statements (see Create a Custom Analyzer), and functions created by CREATE FUNCTION statements:

cr> select routine_name, routine_type
... from information_schema.routines
... group by routine_name, routine_type
... order by routine_name asc limit 5;
+----------------------+--------------+
| routine_name         | routine_type |
+----------------------+--------------+
| PathHierarchy        | TOKENIZER    |
| apostrophe           | TOKEN_FILTER |
| arabic               | ANALYZER     |
| arabic_normalization | TOKEN_FILTER |
| arabic_stem          | TOKEN_FILTER |
+----------------------+--------------+
SELECT 5 rows in set (... sec)

For example you can use this table to list existing tokenizers like this:

cr> select routine_name
... from information_schema.routines
... where routine_type='TOKENIZER'
... order by routine_name asc limit 10;
+---------------+
| routine_name  |
+---------------+
| PathHierarchy |
| char_group    |
| classic       |
| edgeNGram     |
| edge_ngram    |
| keyword       |
| letter        |
| lowercase     |
| nGram         |
| ngram         |
+---------------+
SELECT 10 rows in set (... sec)

Or get an overview of how many routines and routine types are available:

cr> select count(*), routine_type
... from information_schema.routines
... group by routine_type
... order by routine_type;
+----------+--------------+
| count(*) | routine_type |
+----------+--------------+
|       45 | ANALYZER     |
|        3 | CHAR_FILTER  |
|       18 | TOKENIZER    |
|       65 | TOKEN_FILTER |
+----------+--------------+
SELECT 4 rows in set (... sec)

Schema

schemata

The schemata table lists all existing schemas. These schemas are always available: blob, doc, information_schema and sys:

cr> select schema_name from information_schema.schemata order by schema_name;
+--------------------+
| schema_name        |
+--------------------+
| blob               |
| doc                |
| information_schema |
| pg_catalog         |
| sys                |
+--------------------+
SELECT 5 rows in set (... sec)

sql_features

The sql_features table outlines supported and unsupported SQL features of CrateDB based to the current SQL standard (see SQL Standard Compliance):

cr> select feature_name, is_supported, sub_feature_id, sub_feature_name
... from information_schema.sql_features
... where feature_id='F501';
+--------------------------------+--------------+----------------+--------------------+
| feature_name                   | is_supported | sub_feature_id | sub_feature_name   |
+--------------------------------+--------------+----------------+--------------------+
| Features and conformance views | FALSE        |                |                    |
| Features and conformance views | TRUE         | 1              | SQL_FEATURES view  |
| Features and conformance views | FALSE        | 2              | SQL_SIZING view    |
| Features and conformance views | FALSE        | 3              | SQL_LANGUAGES view |
+--------------------------------+--------------+----------------+--------------------+
SELECT 4 rows in set (... sec)

ingestion_rules

The ingestion_rules table contains rules created by CREATE INGEST RULE statements.

Schema