Horton

Re: Should vacuum process config file reload more often

Melanie Plageman <melanieplageman@gmail.com>

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From: Melanie Plageman <melanieplageman@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Masahiko Sawada <sawada.mshk@gmail.com>, Daniel Gustafsson <daniel@yesql.se>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, amit.kapila16@gmail.com
Date: 2023-04-03T22:35:07Z
Lists: pgsql-hackers

Attachments

On Mon, Apr 3, 2023 at 3:08 PM Andres Freund <andres@anarazel.de> wrote:
> On 2023-04-03 14:43:14 -0400, Tom Lane wrote:
> > Melanie Plageman <melanieplageman@gmail.com> writes:
> > > v13 attached with requested updates.
> >
> > I'm afraid I'd not been paying any attention to this discussion,
> > but better late than never.  I'm okay with letting autovacuum
> > processes reload config files more often than now.  However,
> > I object to allowing ProcessConfigFile to be called from within
> > commands in a normal user backend.  The existing semantics are
> > that user backends respond to SIGHUP only at the start of processing
> > a user command, and I'm uncomfortable with suddenly deciding that
> > that can work differently if the command happens to be VACUUM.
> > It seems unprincipled and perhaps actively unsafe.
>
> I think it should be ok in commands like VACUUM that already internally start
> their own transactions, and thus require to be run outside of a transaction
> and at the toplevel. I share your concerns about allowing config reload in
> arbitrary places. While we might want to go there, it would require a lot more
> analysis.

As an alternative for your consideration, attached v14 set implements
the config file reload for autovacuum only (in 0003) and then enables it
for VACUUM and ANALYZE not in a nested transaction command (in 0004).

Previously I had the commits in the reverse order for ease of review (to
separate changes to worker limit balancing logic from config reload
code).

- Melanie

Commits

  1. Fix assertion failure in heap_vacuum_rel

  2. Fix vacuum_cost_delay check for balance calculation.

  3. Fix autovacuum cost debug logging

  4. Refresh cost-based delay params more frequently in autovacuum

  5. Separate vacuum cost variables from GUCs

  6. Make vacuum failsafe_active globally visible

  7. Don't balance vacuum cost delay when per-table settings are in effect