11<!--
2- $PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.346 2005/08/21 03:39:26 tgl Exp $
2+ $PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.347 2005/08/22 17:34:56 momjian Exp $
33-->
44
55<chapter Id="runtime">
@@ -2352,24 +2352,24 @@ archive_command = 'copy "%p" /mnt/server/archivedir/"%f"' # Windows
23522352 </listitem>
23532353 </varlistentry>
23542354
2355- <varlistentry id="guc-enable- constraint-exclusion" xreflabel="enable_constraint_exclusion ">
2356- <term><varname>enable_constraint_exclusion </varname> (<type>boolean</type>)</term>
2355+ <varlistentry id="guc-constraint-exclusion" xreflabel="constraint_exclusion ">
2356+ <term><varname>constraint_exclusion </varname> (<type>boolean</type>)</term>
23572357 <indexterm>
23582358 <primary>constraint exclusion</primary>
23592359 </indexterm>
23602360 <indexterm>
2361- <primary><varname>enable_constraint_exclusion </> configuration parameter</primary>
2361+ <primary><varname>constraint_exclusion </> configuration parameter</primary>
23622362 </indexterm>
23632363 <listitem>
23642364 <para>
2365- Enables or disables the query planner's use of table constraints.
2366- The default is <literal>off</>.
2365+ Enables or disables the query planner's use of table constraints to
2366+ limit table access. The default is <literal>off</>.
23672367 </para>
23682368
23692369 <para>
23702370 When this parameter is <literal>on</>, the planner compares query
2371- conditionsto table CHECK constraints, and omits scanning tables
2372- for which the conditions contradict the constraints. (Presently
2371+ conditionswith table CHECK constraints, and omits scanning tables
2372+ where the conditions contradict the constraints. (Presently
23732373 this is done only for child tables of inheritance scans.) For
23742374 example:
23752375
@@ -2387,15 +2387,15 @@ SELECT * FROM parent WHERE key = 2400;
23872387 </para>
23882388
23892389 <para>
2390- Currently, <varname>enable_constraint_exclusion </> defaults to
2391- <literal>off</>, because itcreates a risk of wrong answers when
2392- query plans are cached: if a table constraint is changed or dropped,
2393- the previously generated planmay now be wrong, and there is no
2390+ Currently, <varname>constraint_exclusion </> defaults to
2391+ <literal>off</>, because itrisks incorrect results if
2392+ query plans are cached --- if a table constraint is changed or dropped,
2393+ the previously generated planmight now be wrong, and there is no
23942394 built-in mechanism to force re-planning. (This deficiency will
23952395 probably be addressed in a future
23962396 <productname>PostgreSQL</productname> release.) Another reason
23972397 for keeping it off is that the constraint checks are relatively
2398- expensive to make , and in many circumstances will yield no savings.
2398+ expensive, and in many circumstances will yield no savings.
23992399 It is recommended to turn this on only if you are actually using
24002400 partitioned tables designed to take advantage of the feature.
24012401 </para>