Re: segment monitoring, stats, histograms

Comments inline.

Goulet, Dick wrote:

>  Wolfgang has his reasons for not liking this approach, and I have to
> agree they are very significant and make sense.  Basically it's a "if
> it's not broke, then don't fix it" approach. 

This "if it ain't broke, don't fix it" of mine extents to the practice 
of gathering statistics. If what you have implemented works for you, 
then leave it alone. DON'T "fix" it, least of all because I said 
something based on my experiences. All I am trying to advocate is 
caution when implementing a new approach and think of the costs, 
benefits and risks. If the risks and costs outnumber the benefits then 
think again.

> 
> I would highly recommend evaluating both approaches at your location.
 > Mine works here and Wolfgang's has been proven not to.
My approach is not "not to analyze". It is to leave the statistics alone 
as much as possible. If some bad plans develop I investigate and if it 
is due to (really) stale statistics then I will re-analyze. If 
statistics of a particular table frequently go stale and cause 
performance problems I will analyze why and implement a strategy that 
fits those circumstances, and that may very well at that point involve 
monitoring the table and base the need to analyze on a determination of 
staleness from that usage pattern. But that could mean that much less 
than 10% modifications trigger "staleness", or just one of the DML 
operations (only inserts, or updates, or deletes, or any combination of 
two).
You could say that I am inherently lazy. If doing nothing is not causing 
any problems, then I choose to do nothing rather than doing something 
and risk that I have to do more to undo it.
If that doing nothing IS causing problems, then I get off my butt and DO 
something about it so I can get back to doing nothing.

> Each site, each database instance, may function differently &
> consequently require a different approach.  I see it as a part of the
> DBA job to apply the approach that works best in the respective
> environment.

Amen to that.


-- 
Regards

Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com
--
http://www.freelists.org/webpage/oracle-l

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