Re: number of semaphores and semaphore sets - Mailing list pgsql-docs

Robert Haas wrote:
> On Mon, Mar 21, 2011 at 12:05 PM, Anton Yuzhaninov <citrin@citrin.ru> wrote:
> > This page:
> > http://www.postgresql.org/docs/9.0/interactive/kernel-resources.html
> >
> > has formula:
> > ceil((max_connections + autovacuum_max_workers) / 16)
> >
> > for number of semaphore sets (identifiers).
> >
> > It seems to be wrong (outdated).
> >
> > Correct formula seems to be
> >
> > ceil((max_connections + autovacuum_max_workers + 4) / 16)
> >
> > Semaphore sets created in src/backend/storage/lmgr/proc.c:
> > 1. MaxConnections
> > 2. autovacuum_max_workers + 1
> > 3. NUM_AUXILIARY_PROCS (currently 3)
>
> Yeah, I think you're right.  It appears that nothing material has
> changed here since 8.3, so I'm inclined to back-patch this doc fix
> back that far.
>
> Barring objections, I'll go change this.

I have applied the attached patch and backpatched it to 9.0 and 9.1.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
new file mode 100644
index 5098aad..68ceff1
*** a/doc/src/sgml/runtime.sgml
--- b/doc/src/sgml/runtime.sgml
*************** psql: could not connect to server: No su
*** 604,616 ****
         <row>
          <entry><varname>SEMMNI</></>
          <entry>Maximum number of semaphore identifiers (i.e., sets)</>
!         <entry>at least <literal>ceil((max_connections + autovacuum_max_workers) / 16)</literal></>
         </row>

         <row>
          <entry><varname>SEMMNS</></>
          <entry>Maximum number of semaphores system-wide</>
!         <entry><literal>ceil((max_connections + autovacuum_max_workers) / 16) * 17</literal> plus room for other
applications</>
         </row>

         <row>
--- 604,616 ----
         <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></>
         </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</>
         </row>

         <row>
*************** psql: could not connect to server: No su
*** 685,691 ****
      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) / 16)</>.
      Lowering the number
      of allowed connections is a temporary workaround for failures,
      which are usually confusingly worded <quote>No space
--- 685,691 ----
      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)</>.
      Lowering the number
      of allowed connections is a temporary workaround for failures,
      which are usually confusingly worded <quote>No space