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Clarify STABLE function documentation to highlight how such functions

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can be optimized.
This commit is contained in:
Bruce Momjian 2006-01-19 22:52:08 +00:00
parent efbe674e4e
commit 807cb000f6
1 changed files with 8 additions and 8 deletions
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16
doc/src/sgml/xfunc.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.109 2005/11/29 01:46:54 alvherre Exp $
$PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.110 2006/01/19 22:52:08 momjian Exp $
-->
<sect1 id="xfunc">
@ -899,13 +899,13 @@ CREATE FUNCTION test(int, int) RETURNS int
<para>
A <literal>STABLE</> function cannot modify the database and is
guaranteed to return the same results given the same arguments
for all calls within a single surrounding query. This category
allows the optimizer to optimize away multiple calls of the function
within a single query. In particular, it is safe to use an expression
containing such a function in an index scan condition. (Since an
index scan will evaluate the comparison value only once, not once at
each row, it is not valid to use a <literal>VOLATILE</> function in
an index scan condition.)
for all rows within a single statement. This category allows the
optimizer to optimize multiple calls of the function to a single
call. In particular, it is safe to use an expression containing
such a function in an index scan condition. (Since an index scan
will evaluate the comparison value only once, not once at each
row, it is not valid to use a <literal>VOLATILE</> function in an
index scan condition.)
</para>
</listitem>
<listitem>