From 2c63b0930aee1bb5c265fad4a65c9d0b62b1f9da Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Tue, 23 Aug 2022 09:55:37 -0400 Subject: [PATCH] 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 --- doc/src/sgml/runtime.sgml | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml index b9c4e611aa..c9b3ea4305 100644 --- a/doc/src/sgml/runtime.sgml +++ b/doc/src/sgml/runtime.sgml @@ -1318,6 +1318,22 @@ default:\ linkend="guc-max-files-per-process"/> configuration parameter to limit the consumption of open files. + + + 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 Resource temporarily unavailable or + Connection refused. The default queue length limit is 128 + on many platforms. To raise it, adjust the appropriate kernel parameter + via sysctl, then restart the postmaster. + The parameter is variously named net.core.somaxconn + on Linux, kern.ipc.soacceptqueue on newer FreeBSD, + and kern.ipc.somaxconn on macOS and other BSD + variants. +