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enable_constraint_exclusion => constraint_exclusion

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Also improve wording.
This commit is contained in:
Bruce Momjian
2005-08-22 17:35:03 +00:00
parent 8ad3965a11
commit a7f49252d2
8 changed files with 31 additions and 33 deletions
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4
doc/src/FAQ/TODO.html
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@ -355,7 +355,7 @@ first.
</p>
</li><li>Add GUC to issue notice about queries that use unjoined tables
</li><li>Allow EXPLAIN to identify tables that were skipped because of
enable_constraint_exclusion
constraint_exclusion
</li><li>Allow EXPLAIN output to be more easily processed by scripts
</li><li>CREATE
<ul>
@ -694,7 +694,7 @@ first.
</li><li>Allow the creation of indexes with mixed ascending/descending specifiers
</li><li>-<em>Fix incorrect rtree results due to wrong assumptions about "over"</em>
operator semantics
</li><li>Allow enable_constraint_exclusion to work for UNIONs like it does for
</li><li>Allow constraint_exclusion to work for UNIONs like it does for
inheritance, and allow it to work for UPDATE and DELETE queries
</li><li>GIST
<ul>

26
doc/src/sgml/runtime.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.346 2005/08/21 03:39:26 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.347 2005/08/22 17:34:56 momjian Exp $
-->
<chapter Id="runtime">
@ -2352,24 +2352,24 @@ archive_command = 'copy "%p" /mnt/server/archivedir/"%f"' # Windows
</listitem>
</varlistentry>
<varlistentry id="guc-enable-constraint-exclusion" xreflabel="enable_constraint_exclusion">
<term><varname>enable_constraint_exclusion</varname> (<type>boolean</type>)</term>
<varlistentry id="guc-constraint-exclusion" xreflabel="constraint_exclusion">
<term><varname>constraint_exclusion</varname> (<type>boolean</type>)</term>
<indexterm>
<primary>constraint exclusion</primary>
</indexterm>
<indexterm>
<primary><varname>enable_constraint_exclusion</> configuration parameter</primary>
<primary><varname>constraint_exclusion</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
Enables or disables the query planner's use of table constraints.
The default is <literal>off</>.
Enables or disables the query planner's use of table constraints to
limit table access. The default is <literal>off</>.
</para>
<para>
When this parameter is <literal>on</>, the planner compares query
conditions to table CHECK constraints, and omits scanning tables
for which the conditions contradict the constraints. (Presently
conditions with table CHECK constraints, and omits scanning tables
where the conditions contradict the constraints. (Presently
this is done only for child tables of inheritance scans.) For
example:
@ -2387,15 +2387,15 @@ SELECT * FROM parent WHERE key = 2400;
</para>
<para>
Currently, <varname>enable_constraint_exclusion</> defaults to
<literal>off</>, because it creates a risk of wrong answers when
query plans are cached: if a table constraint is changed or dropped,
the previously generated plan may now be wrong, and there is no
Currently, <varname>constraint_exclusion</> defaults to
<literal>off</>, because it risks incorrect results if
query plans are cached --- if a table constraint is changed or dropped,
the previously generated plan might now be wrong, and there is no
built-in mechanism to force re-planning. (This deficiency will
probably be addressed in a future
<productname>PostgreSQL</productname> release.) Another reason
for keeping it off is that the constraint checks are relatively
expensive to make, and in many circumstances will yield no savings.
expensive, and in many circumstances will yield no savings.
It is recommended to turn this on only if you are actually using
partitioned tables designed to take advantage of the feature.
</para>