| From: | Darafei "Komяpa" Praliaskouski <me(at)komzpa(dot)net> |
|---|---|
| To: | Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru> |
| Cc: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, Peter Geoghegan <pg(at)bowt(dot)ie>, Andres Freund <andres(at)anarazel(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, "Ideriha, Takeshi" <ideriha(dot)takeshi(at)jp(dot)fujitsu(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com>, pgsql-hackers-owner(at)postgresql(dot)org |
| Subject: | Re: [HACKERS] GUC for cleanup indexes threshold. |
| Date: | 2018-06-16 20:23:17 |
| Message-ID: | CAC8Q8tJCb=gxhzcV7T6ctx7PY-Ux1oA-AsTJc6cAVNsQiYcCzA@mail.gmail.com |
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| Lists: | pgsql-hackers |
Hi!
It is cool to see this in Postgres 11. However:
> 4) vacuum_cleanup_index_scale_factor can be set either by GUC or
> reloption.
> Default value is 0.1. So, by default cleanup scan is triggered after
> increasing of
> table size by 10%.
>
vacuum_cleanup_index_scale_factor can be set to the maximum of 100.
I imagine that on a large append-only table with IOPS storage system budget
it may happen that I would want to never perform a full scan on index.
Roughly, with parameter set to 100, if we vacuum the table first time with
1 tuple and 130 byte wide rows, we'll have a full scan at 130 bytes, 12
kbytes, 1.2MB, 123MB, 12 GB, 1.2TB.
If we happen to perform the first vacuum when there are 4 tuples in the
table, it becomes 52kb, 5MB, 495MB, 48GB - and both 12GB and 48GB will
exhaust any storage spike IOPS budget, slowing everything down rather
suddenly.
Can the upper limit for this GUC be lifted, or have a value for "never"?
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