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Correct the formulas for System V IPC parameters SEMMNI and SEMMNS in docs.

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In runtime.sgml, the old formulas for calculating the reasonable
values of SEMMNI and SEMMNS were incorrect. They have forgotten to
count the number of semaphores which both the checkpointer process
(introduced in 9.2) and the background worker processes (introduced
in 9.3) need.

This commit fixes those formulas so that they count the number of
semaphores which the checkpointer process and the background worker
processes need.

Report and patch by Kyotaro Horiguchi. Only the patch for 9.3 was
modified by me. Back-patch to 9.2 where the checkpointer process was
added and the number of needed semaphores was increased.

Author: Kyotaro Horiguchi
Reviewed-by: Fujii Masao
Backpatch: 9.2
Discussion: http://www.postgresql.org/message-id/20160203.125119.66820697.horiguchi.kyotaro@lab.ntt.co.jp
This commit is contained in:
Fujii Masao 2016-02-16 14:49:47 +09:00
parent 851636bfda
commit 597f7e3a6e
1 changed files with 8 additions and 6 deletions
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14
doc/src/sgml/runtime.sgml
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@ -680,13 +680,13 @@ psql: could not connect to server: No such file or directory
<row>
<entry><varname>SEMMNI</></>
<entry>Maximum number of semaphore identifiers (i.e., sets)</>
<entry>at least <literal>ceil((max_connections + autovacuum_max_workers + 4) / 16)</literal></>
<entry>at least <literal>ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16)</literal></>
</row>
<row>
<entry><varname>SEMMNS</></>
<entry>Maximum number of semaphores system-wide</>
<entry><literal>ceil((max_connections + autovacuum_max_workers + 4) / 16) * 17</literal> plus room for other applications</>
<entry><literal>ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16) * 17</literal> plus room for other applications</>
</row>
<row>
@ -734,20 +734,22 @@ psql: could not connect to server: No such file or directory
<para>
<productname>PostgreSQL</> uses one semaphore per allowed connection
(<xref linkend="guc-max-connections">) and allowed autovacuum worker
process (<xref linkend="guc-autovacuum-max-workers">), in sets of 16.
(<xref linkend="guc-max-connections">), allowed autovacuum worker process
(<xref linkend="guc-autovacuum-max-workers">) and allowed background
process (<xref linkend="guc-max-worker-processes">), in sets of 16.
Each such set will
also contain a 17th semaphore which contains a <quote>magic
number</quote>, to detect collision with semaphore sets used by
other applications. The maximum number of semaphores in the system
is set by <varname>SEMMNS</>, which consequently must be at least
as high as <varname>max_connections</> plus
<varname>autovacuum_max_workers</>, plus one extra for each 16
<varname>autovacuum_max_workers</> plus <varname>max_worker_processes</>,
plus one extra for each 16
allowed connections plus workers (see the formula in <xref
linkend="sysvipc-parameters">). The parameter <varname>SEMMNI</>
determines the limit on the number of semaphore sets that can
exist on the system at one time. Hence this parameter must be at
least <literal>ceil((max_connections + autovacuum_max_workers + 4) / 16)</>.
least <literal>ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16)</>.
Lowering the number
of allowed connections is a temporary workaround for failures,
which are usually confusingly worded <quote>No space