Re: Index sample size when gathering table statistics
From: Stefan Koehler <contact_at_soocs.de>
Date: Sat, 13 Jul 2019 11:29:22 +0200 (CEST)
Message-ID: <126672028.747010.1563010162756_at_ox.hosteurope.de>
Date: Sat, 13 Jul 2019 11:29:22 +0200 (CEST)
Message-ID: <126672028.747010.1563010162756_at_ox.hosteurope.de>
Hello Amir,
I think these 2 blog posts might answer your question.
- https://blogs.oracle.com/optimizer/how-does-autosamplesize-work-in-oracle-database-11g (Section "Effect of auto sample size on index stats gathering")
- https://blogs.oracle.com/optimizer/how-does-auto_sample_size-work-in-oracle-database-12c (Section "Effect of auto sample size on index stats gathering")
However if you wanna know in detail you can also trace DBMS_STATS and have a look at your own ( https://www.pythian.com/blog/options-for-tracing-oracle-dbms_stats/ ).
Best Regards
Stefan Koehler
Independent Oracle performance consultant and researcher
Website: http://www.soocs.de
Twitter: _at_OracleSK
> "Hameed, Amir" <Amir.Hameed_at_xerox.com> hat am 12. Juli 2019 um 16:39 geschrieben:
>
> I am curious to know why Oracle is collecting statistics on indexes this way in 11.2.0.4 where it is using a sample size of 100% on some indexes and a very little sample size on the other.
>
> Thank you,
> Amir
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