RE: When stats trash your performance
- From: "Charudatta Joshi" <joshic@xxxxxxxxxxxxxx>
- To: <malcolmarnold@xxxxxxxxx>
- Date: Thu, 8 Dec 2005 14:52:00 +0530
Malcolm,
Good point about backing up stats which wasn't mentioned before in this
thread. I will just pitch it stronger:
NEVER start gathering statistics until you have exported the earlier
stats.
Stephen, have you checked if the person gathering stats had exported the
earlier ones by any chance? Also, there might be chance of getting the
original stats from your last backup, if you can restore it on a
different host.
Mark Farnham's solution based on a repository of SQL queries is very
nice. In fact a full-fledged product could be constructed on that
concept.
Regards,
Charu.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of malcolm arnold
Sent: 07 December 2005 22:01
To: sollig@xxxxxxxxxxxxx
Cc: stephenbooth.uk@xxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Subject: Re: When stats trash your performance
I agree that changes to statistics should adhere to the same change
management procedure as application code.
As a general point, I think that it is more important to have consistent
response times than the best possible response times in a production
environment.
I also think that it is a good idea to backup your statistics (using
dbms_stats.export_*_stats) as first step of any statistic regathering
procedure, so you have the capability to put things back if it all goes
horribly wrong.
Malcolm.
On 07/12/05, Steve Ollig <sollig@xxxxxxxxxxxxx> wrote:
>
> Stephen -
>
> I believe the reasoning behind that school of thought is that
> statistics should adhere to normal change management procedures just
> as application code would. You wouldn't sling a code change into
> production without running it through a well defined QA process. Why
> wouldn't you do the same with statistics?
>
> -----Original Message-----
> From: oracle-l-bounce@xxxxxxxxxxxxx
> [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On
> Behalf Of stephen booth
> Sent: Wednesday, December 07, 2005 12:59 PM
> To: oracle-l@xxxxxxxxxxxxx
> Subject: When stats trash your performance
>
> I've heard mention in a number of talks that you shouldn't gather
> stats very often, even not at all once a system is bedded in, as it
> can cause your database to start performing really badly. I don't
> recall any one ever saying, or ever reading, an explanation as to why
this might happen.
> Perhaps I'm looking at it from the wrong perspective but it seems
> axiomic that the fresher your stats the better decisions CBO is likely
to make.
>
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