<!-- $PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.423 2008/12/16 19:30:43 alvherre Exp $ -->

<!-- $PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.424 2008/12/18 17:03:09 momjian Exp $ -->

<chapter Id="runtime">

<title>Operating System Environment</title>

<table id="shared-memory-parameters">

<title>Configuration parameters affecting

<productname>PostgreSQL</productname>'s shared memory usage</>

<title><productname>PostgreSQL</productname> shared memory usage</>

<tgroup cols="2">

<thead>

<row>

<entry>Name</>

<entry>Approximatemultiplier (bytesper increment)as of 8.3</>

<entry>Usage</>

<entry>Approximateshared memorybytesrequired (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>

<entry>Connections</>

<entry>(1800 + 270 * <xref

linkend="guc-max-locks-per-transaction">) * <xref

linkend="guc-max-connections"></entry>

</row>

<row>

<entry><xref linkend="guc-autovacuum-max-workers"></>

<entry>1800 + 270 * <xref linkend="guc-max-locks-per-transaction"></entry>

<entry>Autovacuum workers</>

<entry>(1800 + 270 * <xref

linkend="guc-max-locks-per-transaction">) * <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"></entry>

<entry>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>8400 (assuming 8 kB <symbol>BLCKSZ</>)</entry>

<entry>Shared diskbuffers</>

<entry>(<xref linkend="guc-block-size"> + 208) * <xref linkend="guc-shared-buffers"></entry>

</row>

<row>

<entry><xref linkend="guc-wal-buffers"></>

<entry>8200 (assuming 8 kB <symbol>XLOG_BLCKSZ</>)</entry>

<entry>WALbuffers</>

<entry>(<xref linkend="guc-wal-block-size"> + 8) * <xref linkend="guc-wal-buffers"></entry>

</row>

<row>

</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>