Manage Optimizer Statistics with Data Warehouse Workloads

Autonomous Database with Data Warehouse workloads gathers optimizer statistics automatically for tables loaded with direct path operations issued in SQL (direct path load operations that bypass the SQL data processing, such as SQL*Loader direct path, do not collect statistics). For example, for loads using the DBMS_CLOUD package the database gathers optimizer statistics automatically.

If you have tables modified using conventional DML operations you can run commands to gather optimizer statistics for those tables. For example, for the SH schema you can gather statistics for all tables in the schema using the following command:

BEGIN
  DBMS_STATS.GATHER_SCHEMA_STATS('SH', options=>'GATHER AUTO');
END;
/

This example gathers statistics for all tables that have stale statistics in the SH schema.

For more information about direct-path loads see Loading Tables.

For more information on optimizer statistics see Database Concepts.

Manage Optimizer Hints with Data Warehouse Workloads

Autonomous Database with Data Warehouse ignores optimizer hints and PARALLEL hints in SQL statements by default. If your application relies on hints you can enable optimizer hints by setting the parameter OPTIMIZER_IGNORE_HINTS to FALSE at the session or system level using ALTER SESSION or ALTER SYSTEM. For example, the following command enables hints in your session:

ALTER SESSION
   SET OPTIMIZER_IGNORE_HINTS=FALSE;

You can also enable PARALLEL hints in your SQL statements by setting OPTIMIZER_IGNORE_PARALLEL_HINTS to FALSE at the session or system level using ALTER SESSION or ALTER SYSTEM. For example, the following command enables PARALLEL hints in your session:

ALTER SESSION 
   SET OPTIMIZER_IGNORE_PARALLEL_HINTS=FALSE;

Manage Optimizer Statistics with Transaction Processing and JSON Database Workloads

Autonomous Database gathers optimizer statistics automatically so that you do not need to perform this task manually and this helps to ensure your statistics are current. Automatic statistics gathering is enabled in Autonomous Database and runs in a standard maintenance window.

For more information on automatic statistics gathering maintenance window times and automatic optimizer statistics collection, see Database Administrator’s Guide.

For more information on optimizer statistics see SQL Tuning Guide.

Manage Optimizer Hints with Transaction Processing and JSON Database Workloads

Autonomous Database with Transaction Processing and JSON Database workloads honors optimizer hints and PARALLEL hints in SQL statements by default. You can disable optimizer hints by setting the parameter OPTIMIZER_IGNORE_HINTS to TRUE at the session or system level using ALTER SESSION or ALTER SYSTEM. For example, the following command disables hints in your session:

ALTER SESSION
   SET OPTIMIZER_IGNORE_HINTS=TRUE;

You can also disable PARALLEL hints in your SQL statements by setting OPTIMIZER_IGNORE_PARALLEL_HINTS to TRUE at the session or system level using ALTER SESSION or ALTER SYSTEM.

ALTER SESSION 
   SET OPTIMIZER_IGNORE_PARALLEL_HINTS=TRUE;