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Add a note to the CREATE INDEX reference page about the impact of 

maintenance_work_mem and effective_cache_size on index creation speed.
This commit is contained in:
Tom Lane 2008-03-16 23:57:51 +00:00
parent 787eba734b
commit ff213239c5
1 changed files with 19 additions and 2 deletions
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21
doc/src/sgml/ref/create_index.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_index.sgml,v 1.66 2007/11/26 21:36:33 petere Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/create_index.sgml,v 1.67 2008/03/16 23:57:51 tgl Exp $
PostgreSQL documentation
-->
@ -32,7 +32,7 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] <replaceable class="parameter">name</re
<title>Description</title>
<para>
<command>CREATE INDEX</command> constructs an index <replaceable
<command>CREATE INDEX</command> constructs an index named <replaceable
class="parameter">name</replaceable> on the specified table.
Indexes are primarily used to enhance database performance (though
inappropriate use can result in slower performance).
@ -433,6 +433,23 @@ Indexes:
sort high</>, in queries that depend on indexes to avoid sorting steps.
</para>
<para>
For most index methods, the speed of creating an index is
dependent on the setting of <xref linkend="guc-maintenance-work-mem">.
Larger values will reduce the time needed for index creation, so long
as you don't make it larger than the amount of memory really available,
which would drive the machine into swapping. For hash indexes, the
value of <xref linkend="guc-effective-cache-size"> is also relevant to
index creation time: <productname>PostgreSQL</productname> will use one
of two different hash index creation methods depending on whether the
estimated index size is more or less than <varname>effective_cache_size</>.
For best results, make sure that this parameter is also set to something
reflective of available memory, and be careful that the sum of
<varname>maintenance_work_mem</> and <varname>effective_cache_size</> is
less than the machine's RAM less whatever space is needed by other
programs.
</para>
<para>
Use <xref linkend="sql-dropindex" endterm="sql-dropindex-title">
to remove an index.