Horton

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

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, Peter Geoghegan <pg@bowt.ie>, pgsql-hackers@postgresql.org, Robert Haas <robertmhaas@gmail.com>
Date: 2023-04-03T05:09:37Z
Lists: pgsql-hackers 
On Sat, 1 Apr 2023 at 13:24, Melanie Plageman <melanieplageman@gmail.com> wrote:
> Your diff LGTM.
>
> Earlier upthread in [1], Bharath had mentioned in a review comment about
> removing the global variables that he would have expected the analogous
> global in analyze.c to also be removed (vac_strategy [and analyze.c also
> has anl_context]).
>
> I looked into doing this, and this is what I found out (see full
> rationale in [2]):
>
> > it is a bit harder to remove it from analyze because acquire_func
> > doesn't take the buffer access strategy as a parameter and
> > acquire_sample_rows uses the vac_context global variable to pass to
> > table_scan_analyze_next_block().
>
> I don't know if this is worth mentioning in the commit removing the
> other globals? Maybe it will just make it more confusing...

I did look at that, but it seems a little tricky to make work unless
the AcquireSampleRowsFunc signature was changed. To me, it just does
not seem worth doing that to get rid of the two globals in analyze.c.

I pushed the patch with just the vacuum.c changes.

David

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