Gather stats (Oracle) question

[Volker Borowski]

Well,

"setting" the statistcs helps a lot if you have a QA-System with less data than production and you try to track down execution plans on PRD with less data in QA. You select the PRD stats and set them in QA and have a better chance that the behavior is more equal. But you can not set all what influences the optimizer i.e. the index clustering factor might show the optimizer that someone is playing tricks.

If you google around a bit for optimizer and "set statistics" stuff, you'll sure find some presentation-slide of performance-consultants with examples. This is where I got mine (But as said, I am out of office for a while).

I would not go this way (setting stats) in general in production, may be just in single selected cases.

Your described effect that "histogramms helped" might be related to the bug I mentioned! Was that below 9.2.0.6 ?
I doubt that a general calculation of histograms on all tables is of help. They cost in terms of parsing time, because they have to be considered, and select-performance on several systemtables and they are of use only in some special cases, so I would not go and calculate histograms on the entire DB.

Any way good luck in hunting "gets" and "reads"
Volker

[TwoProc]

Well, after playing with this for some time, I 've found a handful of good queries that have responded well to some histograms, and testing has proven that as Volker said - I need to recalculate my statistics with column specifics to refresh histograms properly, and have put them in jobs to get it done on a regular basis(where needed).

Thanks all for the help, it is much appreciated.