| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [PoC] Improve dead tuple storage for lazy vacuum |
| Date: | 2021-07-29 19:14:24 |
| Message-ID: | 20210729191424.lzo27vtqf3umijdq@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2021-07-29 13:15:53 -0400, Robert Haas wrote:
> I don't know if this is better, but I do kind of like the fact that
> the basic representation is just an array. It makes it really easy to
> predict how much memory will be needed for a given number of dead
> TIDs, and it's very DSM-friendly as well.
I think those advantages are far outstripped by the big disadvantage of
needing to either size the array accurately from the start, or to
reallocate the whole array. Our current pre-allocation behaviour is
very wasteful for most vacuums but doesn't handle large work_mem at all,
causing unnecessary index scans.
Greetings,
Andres Freund
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