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Doc: document possible need to raise kernel's somaxconn limit.

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On fast machines, it's possible for applications such as pgbench
to issue connection requests so quickly that the postmaster's
listen queue overflows in the kernel, resulting in unexpected
failures (with not-very-helpful error messages).  Most modern OSes
allow the queue size to be increased, so document how to do that.

Per report from Kevin McKibbin.

Discussion: https://postgr.es/m/CADc_NKg2d+oZY9mg4DdQdoUcGzN2kOYXBu-3--RW_hEe0tUV=g@mail.gmail.com
This commit is contained in:
Tom Lane 2022-08-23 09:55:37 -04:00
parent 4ee6740167
commit ba94dfd4c4
1 changed files with 16 additions and 0 deletions
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doc/src/sgml/runtime.sgml
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@ -1299,6 +1299,22 @@ default:\
linkend="guc-max-files-per-process"/> configuration parameter to
limit the consumption of open files.
</para>
<para>
Another kernel limit that may be of concern when supporting large
numbers of client connections is the maximum socket connection queue
length. If more than that many connection requests arrive within a very
short period, some may get rejected before the postmaster can service
the requests, with those clients receiving unhelpful connection failure
errors such as <quote>Resource temporarily unavailable</quote> or
<quote>Connection refused</quote>. The default queue length limit is 128
on many platforms. To raise it, adjust the appropriate kernel parameter
via <application>sysctl</application>, then restart the postmaster.
The parameter is variously named <varname>net.core.somaxconn</varname>
on Linux, <varname>kern.ipc.soacceptqueue</varname> on newer FreeBSD,
and <varname>kern.ipc.somaxconn</varname> on macOS and other BSD
variants.
</para>
</sect2>
<sect2 id="linux-memory-overcommit">