From: | Kyotaro HORIGUCHI <kyota(dot)horiguchi(at)gmail(dot)com> |
---|---|
To: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Reduce maximum error in tuples estimation after vacuum. |
Date: | 2013-06-14 09:16:42 |
Message-ID: | CAM103DtoF++yuDsMQwZixW0WiVP0eMeWgLen+HofC9N0esVmZA@mail.gmail.com |
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Lists: | pgsql-hackers |
Sorry, I made an mistake.
"Kyotaro HORIGUCHI" <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>:
> Overall algorithm could be illistrated as below,
>
> - summing up used bytes, max offnum(PageGetMaxOffsetNumber),
Not "max" offnum, the number of linp's used after page vacuum.
> maximum free bytes for tuple data , and free bytes after page
> vacuum through all scanned pages.
>
> - summing up free bytes informed by FSM through all skipped
> pages.
>
> - Calculate mean tuple length from the overall used bytes and
> sum of max offnums, and scanned pages.
Here also is the same. not sum of max offnum but total of used
entrre(linp)s.
> - Guess tuple density in skipped pages using overall free bytes
> from FSM and the mean tuple length calculated above.
>
> - Finally, feed estimated number of the live tuples BEFORE
> vacuum into vac_estimate_reltuples.
regards,
--
Kyotaro Horiguchi
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