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From: Bruce Momjian <bruce@momjian.us>
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Subject: Re: [ADMIN] shared_buffers and shmmax
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To: Alvaro Herrera <alvherre@commandprompt.com>
Date: Tue, 16 Dec 2008 17:06:53 -0500 (EST)
CC: Tom Lane <tgl@sss.pgh.pa.us>, valiouk@yahoo.co.uk,
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Alvaro Herrera wrote:
> Alvaro Herrera wrote:
> > Bruce Momjian wrote:
> > 
> > > OK, I never got the change applied because of Alvaro's objection so
> > > there is nothing to revert.   Alvaro said he has an idea for improved
> > > wording;  I do not.
> > 
> > I think we should add a more explicit note, like in the attached patch.
> 
> Committed.  Bruce told me on IM he still wants to do more changes.
> 
> -- 
> Alvaro Herrera                                http://www.CommandPrompt.com/
> The PostgreSQL Company - Command Prompt, Inc.

OK, updated patch.  I added item descriptions and removed Alvaro's
paragraph;  I worked with Alvaro on this patch.

You can see the output in table 17-2:

	http://momjian.us/tmp/pgsql/kernel-resources.html

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

  + If your life is a hard drive, Christ can be your backup. +

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Index: doc/src/sgml/runtime.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v
retrieving revision 1.423
diff -c -c -r1.423 runtime.sgml
*** doc/src/sgml/runtime.sgml	16 Dec 2008 19:30:43 -0000	1.423
--- doc/src/sgml/runtime.sgml	16 Dec 2008 22:01:14 -0000
***************
*** 1087,1141 ****
       <thead>
        <row>
         <entry>Name</>
!        <entry>Approximate multiplier (bytes per increment) as of 8.3</>
        </row>
       </thead>
  
       <tbody>
        <row>
         <entry><xref linkend="guc-max-connections"></>
!        <entry>1800 + 270 * <xref linkend="guc-max-locks-per-transaction"></entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-autovacuum-max-workers"></>
!        <entry>1800 + 270 * <xref linkend="guc-max-locks-per-transaction"></entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-max-prepared-transactions"></>
!        <entry>770 + 270 * <xref linkend="guc-max-locks-per-transaction"></entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-shared-buffers"></>
!        <entry>8400 (assuming 8 kB <symbol>BLCKSZ</>)</entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-wal-buffers"></>
!        <entry>8200 (assuming 8 kB <symbol>XLOG_BLCKSZ</>)</entry>
        </row>
  
        <row>
         <entry>Fixed space requirements</>
!        <entry>770 kB</entry>
        </row>
       </tbody>
      </tgroup>
     </table>
  
!    <note>
!     <para>
!      The multipliers for <varname>shared_buffers</> and
!      <varname>wal_buffers</> should be the number of buffers, not the
!      amount in bytes.  To find out the number of shared or wal buffers, divide
!      the amount in bytes by <xref linkend="guc-block-size"> and
!      <xref linkend="guc-wal-block-size">, respectively.
!     </para>
!    </note>
!   </sect2>
! 
  
    <sect2>
     <title>Resource Limits</title>
--- 1087,1137 ----
       <thead>
        <row>
         <entry>Name</>
!        <entry>Shared memory requirements, as of 8.3</>
        </row>
       </thead>
  
       <tbody>
        <row>
         <entry><xref linkend="guc-max-connections"></>
!        <entry>1800 + 270 * <xref
!        linkend="guc-max-locks-per-transaction"> bytes per connection</entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-autovacuum-max-workers"></>
!        <entry>1800 + 270 * <xref
!        linkend="guc-max-locks-per-transaction"> bytes per worker</entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-max-prepared-transactions"></>
!        <entry>770 + 270 * <xref
!        linkend="guc-max-locks-per-transaction"> bytes per prepared transaction</entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-shared-buffers"></>
!        <entry><xref linkend="guc-block-size"> + 208 bytes per shared buffer</entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-wal-buffers"></>
!        <entry><xref linkend="guc-wal-block-size"> + 8 bytes per WAL buffer</entry>
        </row>
  
        <row>
         <entry>Fixed space requirements</>
!        <entry>770k bytes</entry>
        </row>
       </tbody>
      </tgroup>
     </table>
  
!    <para>
!     These shared memory allocations are reserved at database server
!     start and remain static.
!    </para>
  
    <sect2>
     <title>Resource Limits</title>

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