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

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

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

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/7951e0d7af98fabec9e9146b409b4c5636932d66

Modified Files
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doc/src/sgml/runtime.sgml | 16 ++++++++++++++++
1 file changed, 16 insertions(+)