Re: Lots of memory allocated when reassigning Large Objects

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Guillaume Lelarge <guillaume(at)lelarge(dot)info>
Cc: Justin Pryzby <pryzby(at)telsasoft(dot)com>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Lots of memory allocated when reassigning Large Objects
Date: 2021-11-29 19:39:14
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Guillaume Lelarge <guillaume(at)lelarge(dot)info> writes:
> I've tried Justin's patch but it didn't help with my memory allocation
> issue. FWIW, I attach the patch I used in v14.

[ looks closer ... ] Ah, that patch is a bit buggy: it fails to do the
right thing in the cases where the loop does a "continue". The attached
revision seems to behave properly.

I still see a small leakage, which I think is due to accumulation of
pending sinval messages for the catalog updates. I'm curious whether
that's big enough to be a problem for Guillaume's use case. (We've
speculated before about bounding the memory used for pending sinval
in favor of just issuing a cache reset when the list would be too
big. But nobody's done anything about it, suggesting that people
seldom have a problem in practice.)

>> DROP OWNED BY likely has similar issues.

> Didn't try it, but it wouldn't be a surprise.

I tried just changing the REASSIGN to a DROP in Justin's example,
and immediately hit

ERROR: out of shared memory
HINT: You might need to increase max_locks_per_transaction.

thanks to the per-object locks we try to acquire. So I'm not
sure that the DROP case can reach an interesting amount of
local memory leaked before it runs out of lock-table space.

regards, tom lane

Attachment Content-Type Size
avoid-leak-in-REASSIGN-OWNED-wip.patch text/x-diff 1.4 KB

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