Horton

Re: Option to not use ringbuffer in VACUUM, using it in failsafe mode

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Peter Geoghegan <pg@bowt.ie>
Cc: pgsql-hackers@postgresql.org, Robert Haas <robertmhaas@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, David Rowley <dgrowleyml@gmail.com>
Date: 2023-01-11T19:18:42Z
Lists: pgsql-hackers 
Hi,

On 2023-01-11 11:06:26 -0800, Peter Geoghegan wrote:
> On Wed, Jan 11, 2023 at 10:58 AM Andres Freund <andres@anarazel.de> wrote:
> > Any idea about the name? The obvious thing is to reference ring buffers in the
> > option name, but that's more of an implementation detail...
> 
> What are the chances that anybody using this feature via a manual
> VACUUM command will also use INDEX_CLEANUP off? It's not really
> supposed to be used routinely, at all. Right? It's just for
> emergencies.

I think it's also quite useful for e.g. vacuuming after initial data loads or
if you need to do a first vacuum after a lot of bloat accumulated due to a
stuck transaction.


> Perhaps it can be tied to INDEX_CLEANUP=off? That makes it hard to get
> just the behavior you want when testing VACUUM, but maybe that doesn't
> matter.

I don't like that - it's also quite useful to disable use of ringbuffers when
you actually need to clean up indexes. Especially when we have a lot of dead
tuples we'll rescan indexes over and over...

Greetings,

Andres Freund

Commits

  1. Add unit to vacuum_buffer_usage_limit value in postgresql.conf.sample.

  2. Improve VACUUM/ANALYZE BUFFER_USAGE_LIMIT docs

  3. Add --buffer-usage-limit option to vacuumdb

  4. Add VACUUM/ANALYZE BUFFER_USAGE_LIMIT option

  5. Move various prechecks from vacuum() into ExecVacuum()

  6. Always make a BufferAccessStrategy for ANALYZE

  7. Rename BufferAccessStrategyData.ring_size to nbuffers

  8. Disable vacuum's use of a buffer access strategy during failsafe

  9. Only make buffer strategy for vacuum when it's likely needed

  10. Remove some global variables from vacuum.c

  11. Doc: add Buffer Access Strategy to the glossary