Quest SQL Optimizer for IBM® DB2® LUW maximizes SQL performance by automating the manual, time-intensive and uncertain process of ensuring that SQL statements are performing as fast as possible. SQL Optimizer analyzes, rewrites, and evaluates SQL statements within multiple database objects, files. With SQL Optimizer, you can analyze and optimize all your problem SQL from multiple sources. SQL Optimizer also provides you a complete index optimization and plan change analysis solution, from index recommendations to simulated index impact analysis, through comparison of multiple SQL access plans.
SQL Optimizer provides you with the following main modules.
SQL Optimizer (including SQL Rewrite and Generate Indexes functions)
Quest SQL Optimizer for IBM® DB2® LUW maximizes SQL performance by automating the manual, time-intensive and uncertain process of ensuring that SQL statements are performing as fast as possible. SQL Optimizer analyzes, rewrites, and evaluates SQL statements within multiple database objects, files. With SQL Optimizer, you can analyze and optimize all your problem SQL from multiple sources. SQL Optimizer also provides you a complete index optimization and plan change analysis solution, from index recommendations to simulated index impact analysis, through comparison of multiple SQL access plans.
SQL Optimizer provides you with the following main modules.
SQL Optimizer (including SQL Rewrite and Generate Indexes functions)
The SQL Rewrite function analyzes the input SQL statement and uses an Artificial Intelligence Engine to produce a group of semantically equivalent versions of the statement, known as SQL alternatives. You can then test run these alternatives in the SQL Optimizer window to determine the best-performing version of the SQL.
Tip: After you run SQL Rewrite, run the Generate Indexes function to add alternatives that incorporate virtual indexes. You can then test run the SQL alternatives along with index-set alternatives to measure performance. See Generate Index-Set Alternatives for more information.
The SQL Rewrite process includes these phases:
Retrieves the access plan and the DB2 optimized text that the DB2 LUW optimizer has chosen for the specific SQL alternative. SQL Rewrite classifies the SQL statement according to characteristics that cause performance problems.
Rewrites the original SQL statement to produce a list of semantically equivalent versions, or SQL alternatives.
Allows the users to test run the original and the SQL alternatives to select which SQL version gives the best performance. For each alternative, Batch Run provides the run time for retrieving all records and for retrieving only the first record. You can use this information to identify which alternative is most suitable for your application.
Executes alternatives against the original SQL and displays the returned data for comparison in the SQL Optimizer window.
The SQL Optimizer provides two different measurements of performance; the run time for retrieving all records and the run time for retrieving the first n records. Both measurements give you an indication on the fastest running SQL statement—but with two different aims. You must understand the use of the SQL statement in the application. Generally, if the SQL statement is used for reports, then you should use the Run for All Record or Batch Run with Run Time Mode set to All Records. If the SQL statement is used for online query, then use the Run for First Record or Batch Run with Run Time Mode set to First n Record.
Note: If the aim of the SQL statement is unknown, then use All Records as a performance indication.
