Performing EXPLAIN

EXPLAIN is a performance tuning command provided by DB2/VM. It shows the access path chosen by the DB2/VM Optimizer for a given SQL request.

As the first step of an analysis, SQL/CA performs EXPLAIN for all SQL statements in the application. It then formats the numerical and encoded SQL EXPLAIN results into an interactive, easily readable analysis report.

SQL/CA further enhances the EXPLAIN results:

- by carrying out additional computations and data substitutions
- by integrating information from the DB2/VM catalogs into the analysis report
- by flagging commands, when their explain results indicate a possible performance exposure
- if our SQL/Monitoring program product has been installed, the latest run-time statistics for the application are included in the analysis report. This allows to compare the execution cost, as estimated by DB2/VM, with the actual execution cost.