Joined: 23 Nov 2006 Posts: 19270 Location: Inside the Matrix
RUNSTATS updates catalog statistics used by the optimizer to determine the fastest path to your data. This provides the best information possible to the optimizer.
When there is any data modification to the user tables, the catalog statistics tables are not automatically modified. A RUNSTATS command has to be performed on tables and indexes so that columns in the catalog tables are updated with the latest information.
It is necessary to provide the optimizer with accurate statistics describing the tablespaces and indexes so that it can choose an efficient access path for processing the data.