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