Re: disable histogram usage at session / statement level

Thank you.

Actually my issue is that in an env where nothing is happening if I gather stats on some particular tables where incremental is enabled and regather them immediately reconstruct 90% of the histograms. I basically hit a bug with the query responsable with the quality of histograms (disabling fix 16726844 eliminates this issue)

În joi, 18 mar. 2021 la 13:20, Noveljic Nenad <nenad.noveljic_at_vontobel.com> a scris:

> «I`m starting to think that actually the best method is to have them
> disabled since the beginning and where is the case create one. (instead of
> taking Maria`s advise to use auto and evaluate where they create issues) -
> not to mention that because of histograms for some tables the incremental
> stats don't work as expected “
>
>
>
> Disabling histograms at the outset and then enabling them explicitly as
> needed might actually work well.
>
>
>
> METHOD_OPT AUTO defeats the purpose of incremental stats, as synopses have
> to be recreated whenever the statistic gather procedure decides to create
> new histograms:
> https://nenadnoveljic.com/blog/incremental-statistics-histogram-pitfall/
>
>
>
> Best regards,
>
>
>
> Nenad
>
>
>
>
>
> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> *On
> Behalf Of *Laurentiu Oprea
> *Sent:* Donnerstag, 18. März 2021 12:10
> *To:* Chinar Aliyev <chinaraliyev_at_gmail.com>
> *Cc:* Jonathan Lewis <jlewisoracle_at_gmail.com>; ORACLE-L (
> oracle-l_at_freelists.org) <oracle-l_at_freelists.org>
> *Subject:* Re: disable histogram usage at session / statement level
>
>
>
> Thanks a lot, yes both methods work fine .
>
>
>
> As a background for my question: I noticed that for a lot of tables the
> stats job computed hybrid histograms on ID or PARENT_ID columns and the
> cardinality estimate for joins using these columns are orders of
> magnitude trillion of rows. Dropping/disabling the histogram resolves the
> estimate to 20-30 millions (the expected cardinality)
>
>
>
> Because there are so many tables I need to take now query by query and do
> a quick evaluation with/without histograms and drop where I see a negative
> impact.
>
>
>
> I`m starting to think that actually the best method is to have them
> disabled since the beginning and where is the case create one. (instead of
> taking Maria`s advise to use auto and evaluate where they create issues) -
> not to mention that because of histograms for some tables the incremental
> stats don't work as expected
>
>
>
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