Performance Issues for SELECT in batch job

Hello guys,

I know there are many opinions about the topic but I'm giving it a try :-)

I'm using a custom report which selects data from tables BSIS and BSAS with non-key field PROJK. This report runs every hour in a batch job.

For optimizing the performance I replaced 'FOR ALL ENTRIES' statement in the SELECT with a self-defined range of wbs elements in the WHERE condition.

Now I'm wondering about what happened. Before the optimization the job runs about 20-30 minutes every hour. The first time with my new logic the jobs ran 40 minutes, but then, after the first run of new logic, the jobs constantely runs only 2 minutes.

How is this possible? The only explanation can be the buffering option? But why does the buffering option only happens with the range in the WHERE condition and not in the FOR ALL ENTRIES statement?

And if its really because of the buffer, what is the trigger for this? On what time the buffer gets resetted?

Any opinions? :-)

Regards

Michael