Re: incremental statistics and histograms

From: Chinar Aliyev <chinaraliyev_at_gmail.com>
Date: Mon, 16 Nov 2020 22:14:57 +0400
Message-ID: <CAEfe=X_q0366nHSbQumSkHk6FD4Qm66XFwt2xrd_Rhzc6cWA3g_at_mail.gmail.com>



Hi Nenad,
There is no way(AFAIK) to prevent approximation statistics from the scratch when histogram has to be created for a partition. Although the synopsis is not used directly to gather/approximate histogram, NDV is needed to identify histogram type, that is why the synopsis data has to be updated in order to get fresh NDV. Also, if once histogram is created for a partition then global histogram is gathered based on partition histogram statistics and no need to gather histograms for unchanged partitions. A few years ago I wrote an article about that:

https://www.oracle.com/technical-resources/articles/maintenance-histograms-db-12c.html

Best Regards

On Mon, Nov 16, 2020 at 7:09 PM Noveljic Nenad <nenad.noveljic_at_vontobel.com> wrote:

> Incremental statistics create synopses for each partition. The optimizer
> then uses synopses for calculating global statistics without having to read
> the partitions where data hasn't changed.
>
>
>
> This makes the calculation of global statistics fast and deterministic.
> Except when the optimizer decides to add a histogram (method_opt column
> size is auto). As a consequence, the synapses have to be calculated from
> scratch, which leads to longer stats gathering times.
>
>
>
> What is your strategy for dealing with this problem?
>
>
>
> Best regards,
>
>
>
> Nenad
>
>
>
> https://nenadnoveljic.com/blog
>
>
>
>
>
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Received on Mon Nov 16 2020 - 19:14:57 CET

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