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: Justin Pryzby <pryzby@telsasoft.com>
Cc: Peter Geoghegan <pg@bowt.ie>, pgsql-hackers@postgresql.org, Robert Haas <robertmhaas@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, David Rowley <dgrowleyml@gmail.com>
Date: 2023-01-11T21:09:42Z
Lists: pgsql-hackers 
Hi,

On 2023-01-11 14:38:34 -0600, Justin Pryzby wrote:
> On Wed, Jan 11, 2023 at 10:58:54AM -0800, Andres Freund wrote:
> > Some ideas:
> > 
> > USE_RING_BUFFERS on|off
> > REUSE_BUFFERS on|off
> 
> +1 for either of these.

Then I'd go for REUSE_BUFFERS. What made you prefer it over
LIMIT_BUFFER_USAGE?

USE_BUFFER_ACCESS_STRATEGY would be a name tied to the implementation that's
not awful, I think..


> I don't think it's an issue to expose implementation details here.
> Anyone who wants to change this will know about the implementation
> details that they're changing, and it's better to refer to it by the
> same/similar name and not by some other name that's hard to find.

A ringbuffer could refer to a lot of things other than something limiting
buffer usage, that's why I don't like it.


> BTW I can't see that the ring buffer is currently exposed in any
> user-facing docs for COPY/ALTER/VACUUM/CREATE ?

Yea, there's surprisingly little in the docs about it, given how much it
influences behaviour. It's mentioned in tablesample-method.sgml, but without
explanation - and it's a page documenting C API...

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