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Re: allow changing autovacuum_max_workers without restarting

Sami Imseih <simseih@amazon.com>

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From: "Imseih (AWS), Sami" <simseih@amazon.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2024-04-18T05:05:03Z
Lists: pgsql-hackers 
> Here is a first attempt at a proper patch set based on the discussion thus
> far. I've split it up into several small patches for ease of review, which
> is probably a bit excessive. If this ever makes it to commit, they could
> likely be combined.

I looked at the patch set. With the help of DEBUG2 output, I tested to ensure
that the the autovacuum_cost_limit  balance adjusts correctly when the 
autovacuum_max_workers value increases/decreases. I did not think the 
patch will break this behavior, but it's important to verify this.

Some comments on the patch:

1. A nit. There should be a tab here.

-       dlist_head      av_freeWorkers;
+       dclist_head av_freeWorkers;

2. autovacuum_max_worker_slots documentation:

+       <para>
+        Note that the value of <xref linkend="guc-autovacuum-max-workers"/> is
+        silently capped to this value.
+       </para>

This comment looks redundant in the docs, since the entry 
for autovacuum_max_workers that follows mentions the
same.


3. The docs for autovacuum_max_workers should mention that when
the value changes, consider adjusting the autovacuum_cost_limit/cost_delay. 

This is not something new. Even in the current state, users should think about 
these settings. However, it seems even important if this value is to be 
dynamically adjusted.


Regards,

Sami

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Give up on running with NetBSD/OpenBSD's default semaphore settings.

  2. initdb: Do not report default autovacuum_worker_slots.

  3. Lower default value of autovacuum_worker_slots in initdb as needed.

  4. Allow changing autovacuum_max_workers without restarting.

  5. Reserve a PGPROC slot and semaphore for the slotsync worker process.

  6. Make archiver process an auxiliary process.

  7. Correct the formulas for System V IPC parameters SEMMNI and SEMMNS in docs.