Re: Race conditions in

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, hlinnaka(at)iki(dot)fi, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Race conditions in
Date: 2022-02-18 22:42:48
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On 2022-02-17 21:55:21 -0800, Andres Freund wrote:
> Isn't it pretty bonkers that we allow error processing to get stuck behind
> network traffic, *before* we have have released resources (locks etc)?

This is particularly likely to be a problem for walsenders, because they often
have a large output buffer filled, because walsender uses
pq_putmessage_noblock() to send WAL data. Which obviously can be large.

In the stacktrace upthread you can see:
#3 0x00007faf4b70f48b in secure_write (port=0x7faf4c22da50, ptr=0x7faf4c2f1210, len=21470) at /home/andres/src/postgresql/src/backend/libpq/be-secure.c:29

which certainly is more than in most other cases of error messages being
sent. And it obviously might not be the first to have gone out.

> I wonder if we should try to send, but do it in a nonblocking way.

I think we should probably do so at least during FATAL error processing. But
also consider doing so for ERROR, because not releasing resources after
getting cancelled / terminated is pretty nasty imo.


Andres Freund

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