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.