OPT_GOAL configuration parameter

Use the OPT_GOAL configuration parameter to specify an optimization goal for queries.

onconfig.std value
OPT_GOAL -1
values
0 or -1
takes effect
After you edit your onconfig file and restart the database server.

Usage

A value of 0 sets the optimization goal to FIRST_ROWS. A value of -1 sets the optimization goal to ALL_ROWS, which is the default.

When you set the optimization goal to optimize for FIRST ROWS, you specify that you want the database server to optimize queries for perceived response time. In other words, users of interactive applications perceive response time as the time that it takes to display data on the screen. Setting the optimization goal to FIRST ROWS configures the database server to return the first rows of data that satisfy the query.

When you set the optimization goal to optimize for ALL ROWS, you specify that you want the database server to optimize for the total execution time of the query. Making ALL ROWS the optimization goal instructs the database server to process the total query as quickly as possible, regardless of how long it takes to return the first rows to the application.

You can specify the optimization goal in one of four ways:
  • By query (SELECT statement)

    Use the ALL_ROWS and FIRST_ROWS directives.

  • By session

    Use the SET OPTIMIZATION statement.

  • By environment

    Set the OPT_GOAL environment variable.

  • By database server

    Set the OPT_GOAL configuration parameter.

The list above lists the mechanisms for setting this goal in descending order of precedence. To determine the optimization goal, the database server examines the settings in the order above. The first setting encountered determines the optimization goal. For example, if a query includes the ALL_ROWS directive but the OPT_GOAL configuration parameter is set to FIRST_ROWS, the database server optimizes for ALL_ROWS, as the query specifies.


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