Release 10.1A: OpenEdge Data Management:
DataServer for ODBC

Query tuning with connection and startup parameters

You can control aspects of DataServer query handling not only programmatically within 4GL statements, but also through startup and connection parameter options as described in this section.

Note: Startup and connection parameters override query-tuning defaults. However, options set in the QUERY–TUNING phrase take precedence over startup and connection parameters. For example, if you specify NO–DEBUG for a query within your application, specifying qt_debug,SQL at connection time overrides the default application behavior but does not override the NO–DEBUG option that you specified for the query. See the "Query tuning" section for more information.

You override query-tuning defaults with the DataServer (-Dsrv) connection parameter when you connect to an ODBC data source. This is the syntax:

Syntax

CONNECT data-source-name -dt ODBC -Dsrv query-tuning-option1,value1 -Dsrv query-tuning-option2,value2.

An alternate syntax for the -Dsrv parameter follows:

Syntax

CONNECT data-source-name -dt ODBC -Dsrv query-tuning-option1,value1,query-tuning-option2,value2.

Table 4–2 describes the query-tuning options that you can specify with the -Dsrv parameter.

Table 4–2: Connection query-tuning options

Option	Description
qt_no_debug qt_debug,SQL qt_debug,EXTENDED qt_debug,CURSOR qt_debug,PERFORMANCE qt_debug,CALL_SUMMARY qt_debug,VERBOSE	Specifies whether the DataServer prints debugging information that it generates for the query to the dataserv.lg file. The default is qt_no_debug, to supply no debugging information. To override the default, specify qt_debug,option as follows: Specify qt_debug,SQL to print the SQL statements that the DataServer executes against the ODBC data source. Specify qt_debug,EXTENDED to print information such as cursor statistics in addition to the SQL statements executed by the DataServer. Specify qt_debug,CURSOR to print information about the cursors that the DataServer uses for internal calls and for opening queries. Specify qt_debug,PERFORMANCE to print information on the amount of time that certain operations take. Specify qt_debug,CALL_SUMMARY to print information on cursors and timing. Specify qt_debug,VERBOSE to print all of the information gathered by the other qt_debug options. For more detailed descriptions of these options, see Table 4–4.
qt_lookahead qt_no_lookahead	Specifies whether the DataServer uses lookahead or standard cursors. Lookahead is the default when you use NO–LOCK in a 4GL statement. When isolation level is set to read-uncommitted, lookahead is also the default whenever the 4GL does not specify EXCLUSIVE–LOCK. Specify qt_no_lookahead for behavior that is consistent with OpenEdge.
qt_separate_connection qt_no_separate_connection	Specifies whether each cursor should use a separate connection to the ODBC data source. The default is qt_no_separate_connection, which provides behavior that is consistent with OpenEdge. Specify qt_separate_connection to use a separate connection. Executing cursors in separate connections can improve performance because the DataServer does not have to restart the cursors.
qt_cache_size,integer	Specifies the size in bytes of the cache used by lookahead cursors. A larger cache size can improve performance for queries that return a large number of records because the DataServer might need fewer SQL statements to get the results. Minimum: The DataServer always caches at least one record. Maximum: None Default: 30000

The following example shows how to use the query-tuning options to enhance performance. The DataServer opens a separate connection to ODBC for each cursor and writes an extended report on the SQL statements it executes:

CONNECT holder -db infdb -dt ODBC -ld demo -U user -P password -Dsrv qt_separate_connection,qt_debug,EXTENDED.

OpenEdge provides a startup parameter called Server Join (-nojoinbysqldb) that controls the default JOIN–BY–SQLDB behavior. You specify this parameter in the startup command for your OpenEdge session. It overrides the JOIN–BY–SQLDB default so that the client evaluates and performs joins. Using this parameter might slow performance, but it provides results that are consistent with OpenEdge behavior. See Chapter 2, "Programming Considerations," for more information.