Synchronous statistics collections

An interesting feature of the RUNSTATS facility – as well as collecting  statistics asynchronously (in the background)  , it can also set a synchronous collection – at statement compilation time

 If the real time statistics is enabled – the optimizer makes the decision. Real statistics collection doesn’t preclude  the background collection – which still happens in the background. The decision to enable real time collection should  be based on application requirements. For example , you probably wouldn’t turn on real time statistics , if there are rarely any UPDATE,DELETE,INSERT statements

 A number of measures are in place to throttle the impact , such as : RUNSTATS is throttled , one synchronous stats collection per table, a table has to have no statistics or high levels of UPDATE,DELETE,INSERT to be considered for collection., in V9.5 a statistics cache is made available to all statements.

 It is useful to monitor the $DIAGPATH/events db2optstats.number.log  file which is a rotating log of all statistics activity on the database

 Ref:Jack Vamvas(http://www.dba-db2.com)