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

MasaoFujii · MasaoFujii · commit 984da963fb45 · 2016-02-16T14:59:19.000+09:00
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
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
@@ -645,13 +645,13 @@ 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 + number of background 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 + number of background processes + 5) / 16) * 17</literal> plus room for other applications</>
        </row>
 
        <row>
@@ -699,20 +699,23 @@ 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 processes requesting shared memory access, 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 number of background
+    processes requesting shared memory access, 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 +
+    number of background processes + 5) / 16)</>.
     Lowering the number
     of allowed connections is a temporary workaround for failures,
     which are usually confusingly worded <quote>No space
