orafce

orafce

The orafce module provides Oracle Compatibility SQL functions in Greenplum Database. These functions target PostgreSQL but can also be used in Greenplum.

The Greenplum Database orafce module is a modified version of the open source Orafce PostgreSQL module extension. The modified orafce source files for Greenplum Database can be found in the gpcontrib/orafce directory in the Greenplum Database open source project. The source reflects the Orafce 3.6.1 release and additional commits to 3af70a28f6.

There are some restrictions and limitations when you use the module in Greenplum Database.

Installing and Registering the Module

Note: Always use the Oracle Compatibility Functions module included with your Greenplum Database version. Before upgrading to a new Greenplum Database version, uninstall the compatibility functions from each of your databases, and then, when the upgrade is complete, reinstall the compatibility functions from the new Greenplum Database release. See the Greenplum Database release notes for upgrade prerequisites and procedures.

The orafce module is installed when you install Greenplum Database. Before you can use any of the functions defined in the module, you must register the orafce extension in each database in which you want to use the functions.

Greenplum Database Considerations

The following functions are available by default in Greenplum Database and do not require installing the Oracle Compatibility Functions:

sinh()
tanh()
cosh()
decode() (See Greenplum Implementation Differences for more information.)

Greenplum Implementation Differences

There are differences in the implementation of the compatibility functions in Greenplum Database from the original PostgreSQL orafce module extension implementation. Some of the differences are as follows:

The original orafce module implementation performs a decimal round off, the Greenplum Database implementation does not:
- 2.00 becomes 2 in the original module implementation
- 2.00 remains 2.00 in the Greenplum Database implementation
The provided Oracle compatibility functions handle implicit type conversions differently. For example, using the decode function:
```
decode(expression, value, return [,value, return]...
            [, default])
```
The original orafce module implementation automatically converts expression and each value to the data type of the first value before comparing. It automatically converts return to the same data type as the first result.

The Greenplum Database implementation restricts return and default to be of the same data type. The expression and value can be different types if the data type of value can be converted into the data type of the expression. This is done implicitly. Otherwise, decode fails with an invalid input syntax error. For example:
```
SELECT decode('a','M',true,false);
CASE
------
 f
(1 row)
SELECT decode(1,'M',true,false);
ERROR: Invalid input syntax for integer:"M" 
LINE 1: SELECT decode(1,'M',true,false);
```
Numbers in bigint format are displayed in scientific notation in the original orafce module implementation but not in the Greenplum Database implementation:
- 9223372036854775 displays as 9.2234E+15 in the original implementation
- 9223372036854775 remains 9223372036854775 in the Greenplum Database implementation

The default date and timestamp format in the original orafce module implementation is different than the default format in the Greenplum Database implementation. If the following code is executed:

CREATE TABLE TEST(date1 date, time1 timestamp, time2 
                  timestamp with time zone);
INSERT INTO TEST VALUES ('2001-11-11','2001-12-13 
                 01:51:15','2001-12-13 01:51:15 -08:00');
SELECT DECODE(date1, '2001-11-11', '2001-01-01') FROM TEST;

The Greenplum Database implementation returns the row, but the original implementation returns no rows.

Note: The correct syntax when using the original orafce implementation to return the row is:

SELECT DECODE(to_char(date1, 'YYYY-MM-DD'), '2001-11-11', 
              '2001-01-01') FROM TEST

The functions in the Oracle Compatibility Functions dbms_alert package are not implemented for Greenplum Database.
The decode() function is removed from the Greenplum Database Oracle Compatibility Functions. The Greenplum Database parser internally converts a decode() function call to a CASE statement.

Using orafce

Some Oracle Compatibility Functions reside in the oracle schema. To access them, set the search path for the database to include the oracle schema name. For example, this command sets the default search path for a database to include the oracle schema:

ALTER DATABASE db_name SET search_path = "$user", public, oracle;

Note the following differences when using the Oracle Compatibility Functions with PostgreSQL vs. using them with Greenplum Database:

If you use validation scripts, the output may not be exactly the same as with the original orafce module implementation.
The functions in the Oracle Compatibility Functions dbms_pipe package execute only on the Greenplum Database master host.
The upgrade scripts in the Orafce project do not work with Greenplum Database.

Additional Module Documentation

Refer to the README and Greenplum Database orafce documentation in the Greenplum Database github repository for detailed information about the individual functions and supporting objects provided in this module.

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