Horton

Re: Why our Valgrind reports suck

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Álvaro Herrera <alvherre@kurilemu.de>
Cc: Andres Freund <andres@anarazel.de>, pgsql-hackers@lists.postgresql.org
Date: 2025-05-12T14:23:56Z
Lists: pgsql-hackers 
=?utf-8?Q?=C3=81lvaro?= Herrera <alvherre@kurilemu.de> writes:
> On 2025-May-11, Tom Lane wrote:
>> In particular, I had not realized that autovacuum
>> leaks a nontrivial amount of memory per relation processed (cf 0009),
>> and apparently has done for a few releases now.  This is horrid in
>> databases with many tables, and I'm surprised that we've not gotten
>> complaints about it.

> In PGConf Germany we got a lightning talk[1] that reported a problem
> that might be explained by this: with 10 million of relations, the OOM
> killer gets invoked on autovacuum workers on the reported case, so
> essentially autovacuum doesn't work at all.  So clearly there is somebody
> that would appreciate that this problem is fixed.

Interesting.

> He actually blames it on relcache, but who knows how correct that is.

I would not be surprised if the relcache is bloated too, but Valgrind
wouldn't think that's a leak.  I wonder if it'd be worth setting up
a mechanism for autovacuum to drop the relcache entry for a table
once it's done with it.

			regards, tom lane

Commits

  1. Undo thinko in commit e78d1d6d4.

  2. Avoid leakage of zero-length arrays in partition_bounds_copy().

  3. Fix MemoryContextAllocAligned's interaction with Valgrind.

  4. Fix assorted pretty-trivial memory leaks in the backend.

  5. Improve our support for Valgrind's leak tracking.

  6. Reduce leakage during PL/pgSQL function compilation.

  7. Silence Valgrind leakage complaints in more-or-less-hackish ways.

  8. Silence complaints about leaks in PlanCacheComputeResultDesc.

  9. Suppress complaints about leaks in TS dictionary loading.

  10. Suppress complaints about leaks in function cache loading.

  11. Fix per-relation memory leakage in autovacuum.

  12. Fix AlignedAllocRealloc to cope sanely with OOM.