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From: Bruce Momjian <bruce@momjian.us>
Message-Id: <200812170133.mBH1Xac23918@momjian.us>
Subject: Re: [ADMIN] shared_buffers and shmmax
In-Reply-To: <17528.1229470697@sss.pgh.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 16 Dec 2008 20:33:36 -0500 (EST)
CC: Alvaro Herrera <alvherre@commandprompt.com>, valiouk@yahoo.co.uk,
	pgsql-docs@postgresql.org, dx k9 <bitsandbytes88@hotmail.com>
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Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > OK, updated patch.  I added item descriptions and removed Alvaro's
> > paragraph;  I worked with Alvaro on this patch.
> 
> This still seems pretty misleading, as for example
>   
> >        <tbody>
> >         <row>
> >          <entry><xref linkend="guc-max-connections"></>
> > !        <entry>1800 + 270 * <xref
> > !        linkend="guc-max-locks-per-transaction"> bytes per connection</entry>
> >         </row>
> 
> sounds like it might mean bytes per *active* connection, when of course
> the correct way to figure it is by multiplying by max_connections.
> If you're going to give a formula, why not just give a formula, eg
> 
> 	(1800 + 270 * max_locks_per_transaction) * (max_connections + autovacuum_max_workers)
> 
> 			regards, tom lane

You mean like this:

	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	17 Dec 2008 01:30:21 -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>
--- 1087,1132 ----
       <thead>
        <row>
         <entry>Name</>
!        <entry>Shared memory bytes required, as of 8.3</>
        </row>
       </thead>
  
       <tbody>
        <row>
!        <entry><xref linkend="guc-max-connections">, <xref linkend="guc-autovacuum-max-workers"></>
!        <entry>(1800 + 270 * <xref
!        linkend="guc-max-locks-per-transaction">) * (<xref
!        linkend="guc-max-connections"> + <xref linkend="guc-autovacuum-max-workers">)</entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-max-prepared-transactions"></>
!        <entry>(770 + 270 * <xref
!        linkend="guc-max-locks-per-transaction">) * <xref linkend="guc-max-prepared-transactions"></entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-shared-buffers"></>
!        <entry>(<xref linkend="guc-block-size"> + 208) * <xref linkend="guc-shared-buffers"></entry>
        </row>
  
        <row>
         <entry><xref linkend="guc-wal-buffers"></>
!        <entry>(<xref linkend="guc-wal-block-size"> + 8) * <xref linkend="guc-wal-buffers"></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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