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<chapter Id="runtime-config">

<title>Server Configuration</title>

This setting must be at least 128 kilobytes. (Non-default

values of <symbol>BLCKSZ</symbol> change the minimum.) However,

settings significantly higher than the minimum are usually needed

for good performance. Several tens of megabytes are recommended

for production installations. This parameter can only be set at

server start.

for good performance. This parameter can only be set at server start.

</para>

<para>

If you have a dedicated database server with 1GB or more of RAM, a

reasonable starting value for <varname>shared_buffers</varname> is 25%

of the memory in your system. There are some workloads where even

large settings for <varname>shared_buffers</varname> are effective, but

because <productname>PostgreSQL</productname> also relies on the

operating system cache, it is unlikely that an allocation of more than

40% of RAM to <varname>shared_buffers</varname> will work better than a

smaller amount. Larger settings for <varname>shared_buffers</varname>

usually require a corresponding increase in

<varname>checkpoint_segments</varname>, in order to spread out the

process of writing large quantities of new or changed data over a

longer period of time.

</para>

<para>

On systems with less than 1GB of RAM, a smaller percentage of RAM is

appropriate, so as to leave adequate space for the operating system.

Also, on Windows, large values for <varname>shared_buffers</varname>

aren't as effective. You may find better results keeping the setting

relatively low and using the operating system cache more instead. The

useful range for <varname>shared_buffers</varname> on Windows systems

is generally from 64MB to 512MB.

</para>

<para>