| From: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com> |
| Cc: | Justin Pryzby <pryzby(at)telsasoft(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Peter Geoghegan <pg(at)bowt(dot)ie>, pgsql-hackers(at)postgresql(dot)org, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: Option to not use ringbuffer in VACUUM, using it in failsafe mode |
| Date: | 2023-04-01 17:29:13 |
| Message-ID: | CAAKRu_bRTy-sCUuFz3HYhz2Z==XArFJCQwmvJaDVFTJUpZKWCg@mail.gmail.com |
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| Lists: | pgsql-hackers |
Hi,
I was just doing some cleanup on the main patch in this set and realized
that it was missing a few things. One of which is forbidding the
BUFFER_USAGE_LIMIT with VACUUM FULL since VACUUM FULL does not use a
BAS_VACUUM strategy.
VACUUM FULL technically uses a bulkread buffer access strategy for
reading the original relation if its number of blocks is > number of
shared buffers / 4 (see initscan()). The new rel writing is done using
smgrextend/write directly and doesn't go through shared buffers. I
think it is a stretch to try and use the size passed in to VACUUM by
BUFFER_USAGE_LIMIT for the bulkread strategy ring.
As for forbidding the combination, I noticed that when VACUUM FULL is
specified with INDEX_CLEANUP OFF, there is no syntax error but the
INDEX_CLEANUP option is simply ignored. This is documented behavior.
I somehow feel like VACUUM (FULL, BUFFER_USAGE_LIMIT 'x') should error
out instead of silently not using the buffer usage limit, though.
I am looking for others' opinions.
- Melanie
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