From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: max_files_per_processes vs others uses of file descriptors |
Date: | 2017-08-07 21:05:06 |
Message-ID: | 22579.1502139906@sss.pgh.pa.us |
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Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2017-08-07 16:52:42 -0400, Tom Lane wrote:
>> No, I don't think so. If you're depending on the NUM_RESERVED_FDS
>> headroom for anything meaningful, *you're doing it wrong*. You should be
>> getting an FD via fd.c, so that there is an opportunity to free up an FD
>> (by closing a VFD) if you're up against system limits. Relying on
>> NUM_RESERVED_FDS headroom can only protect against EMFILE not ENFILE.
> How would this work for libpq based stuff like postgres fdw? Or some
> random PL doing something with files? There's very little headroom here.
Probably the best we can hope for there is to have fd.c provide a function
"close an FD please", which postgres_fdw could call if libpq fails because
of ENFILE/EMFILE, and then retry. (Though I'm unsure how reliably
postgres_fdw can detect that failure reason right now --- I don't know
that we preserve errno on the way out of PQconnect.)
regards, tom lane
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