Add exclusion constraints, which generalize the concept of uniqueness to

support any indexable commutative operator, not just equality.  Two rows
violate the exclusion constraint if "row1.col OP row2.col" is TRUE for
each of the columns in the constraint.

Jeff Davis, reviewed by Robert Haas

Author: tglsfdc

doc/src/sgml/catalogs.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.211 2009/11/20 20:38:09 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.212 2009/12/07 05:22:21 tgl Exp $ -->
 <!--
  Documentation of the system catalogs, directed toward PostgreSQL developers
  -->
@@ -1536,11 +1536,7 @@
       <entry><type>bool</type></entry>
       <entry></entry>
       <entry>
-       True if this is a table and it has (or recently had) any
-       indexes. This is set by <command>CREATE INDEX</command>, but
-       not cleared immediately by <command>DROP INDEX</command>.
-       <command>VACUUM</command> clears <structfield>relhasindex</> if it finds the
-       table has no indexes
+       True if this is a table and it has (or recently had) any indexes
       </entry>
      </row>
 
@@ -1617,6 +1613,17 @@
       </entry>
      </row>
 
+     <row>
+      <entry><structfield>relhasexclusion</structfield></entry>
+      <entry><type>bool</type></entry>
+      <entry></entry>
+      <entry>
+       For a table, true if the table has (or once had) any exclusion
+       constraints; for an index, true if the index supports an exclusion
+       constraint
+      </entry>
+     </row>
+
      <row>
       <entry><structfield>relhasrules</structfield></entry>
       <entry><type>bool</type></entry>
@@ -1680,6 +1687,17 @@
     </tbody>
    </tgroup>
   </table>
+
+  <para>
+   Several of the boolean flags in <structname>pg_class</> are maintained
+   lazily: they are guaranteed to be true if that's the correct state, but
+   may not be reset to false immediately when the condition is no longer
+   true.  For example, <structfield>relhasindex</> is set by
+   <command>CREATE INDEX</command>, but it is never cleared by
+   <command>DROP INDEX</command>.  Instead, <command>VACUUM</command> clears
+   <structfield>relhasindex</> if it finds the table has no indexes.  This
+   arrangement avoids race conditions and improves concurrency.
+  </para>
  </sect1>
 
  <sect1 id="catalog-pg-constraint">
@@ -1690,11 +1708,12 @@
   </indexterm>
 
   <para>
-   The catalog <structname>pg_constraint</structname> stores check, primary key, unique, and foreign
-   key constraints on tables.  (Column constraints are not treated
-   specially.  Every column constraint is equivalent to some table
-   constraint.)  Not-null constraints are represented in the
-   <structname>pg_attribute</> catalog.
+   The catalog <structname>pg_constraint</structname> stores check, primary
+   key, unique, foreign key, and exclusion constraints on tables.
+   (Column constraints are not treated specially.  Every column constraint is
+   equivalent to some table constraint.)
+   Not-null constraints are represented in the <structname>pg_attribute</>
+   catalog, not here.
   </para>
 
   <para>
@@ -1739,7 +1758,8 @@
         <literal>c</> = check constraint,
         <literal>f</> = foreign key constraint,
         <literal>p</> = primary key constraint,
-        <literal>u</> = unique constraint
+        <literal>u</> = unique constraint,
+        <literal>x</> = exclusion constraint
       </entry>
      </row>
 
@@ -1776,7 +1796,7 @@
       <entry><type>oid</type></entry>
       <entry><literal><link linkend="catalog-pg-class"><structname>pg_class</structname></link>.oid</literal></entry>
       <entry>The index supporting this constraint, if it's a unique, primary
-       key, or foreign key constraint; else 0</entry>
+       key, foreign key, or exclusion constraint; else 0</entry>
      </row>
 
      <row>
@@ -1828,7 +1848,7 @@
       <entry><type>bool</type></entry>
       <entry></entry>
       <entry>
-       This constraint is defined locally in the relation.  Note that a
+       This constraint is defined locally for the relation.  Note that a
        constraint can be locally defined and inherited simultaneously
       </entry>
      </row>
@@ -1838,7 +1858,8 @@
       <entry><type>int4</type></entry>
       <entry></entry>
       <entry>
-       The number of direct ancestors this constraint has.  A constraint with
+       The number of direct inheritance ancestors this constraint has.
+       A constraint with
        a nonzero number of ancestors cannot be dropped nor renamed
       </entry>
      </row>
@@ -1878,6 +1899,13 @@
       <entry>If a foreign key, list of the equality operators for FK = FK comparisons</entry>
      </row>
 
+     <row>
+      <entry><structfield>conexclop</structfield></entry>
+      <entry><type>oid[]</type></entry>
+      <entry><literal><link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.oid</></entry>
+      <entry>If an exclusion constraint, list of the per-column exclusion operators</entry>
+     </row>
+
      <row>
       <entry><structfield>conbin</structfield></entry>
       <entry><type>text</type></entry>
@@ -1895,6 +1923,16 @@
    </tgroup>
   </table>
 
+  <para>
+   In the case of an exclusion constraint, <structfield>conkey</structfield>
+   is only useful for constraint elements that are simple column references.
+   For other cases, a zero appears in <structfield>conkey</structfield>
+   and the associated index must be consulted to discover the expression
+   that is constrained.  (<structfield>conkey</structfield> thus has the
+   same contents as <structname>pg_index</>.<structfield>indkey</> for the
+   index.)
+  </para>
+
   <note>
    <para>
     <structfield>consrc</structfield> is not updated when referenced objects
@@ -1908,7 +1946,8 @@
    <para>
     <literal>pg_class.relchecks</literal> needs to agree with the
     number of check-constraint entries found in this table for each
-    relation.
+    relation.  Also, <literal>pg_class.relhasexclusion</literal> must
+    be true if there are any exclusion-constraint entries for the relation.
    </para>
   </note>
 

doc/src/sgml/errcodes.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/errcodes.sgml,v 1.27 2009/03/04 10:55:00 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/errcodes.sgml,v 1.28 2009/12/07 05:22:21 tgl Exp $ -->
 
 <appendix id="errcodes-appendix">
  <title><productname>PostgreSQL</productname> Error Codes</title>
@@ -640,6 +640,12 @@
 <entry>check_violation</entry>
 </row>
 
+<row>
+<entry><literal>23P01</literal></entry>
+<entry>EXCLUSION VIOLATION</entry>
+<entry>exclusion_violation</entry>
+</row>
+
 
 <row>
 <entry spanname="span13"><emphasis role="bold">Class 24 &mdash; Invalid Cursor State</></entry>