Fix docs on lock level for ALTER TABLE VALIDATE

ALTER TABLE .. VALIDATE CONSTRAINT previously
gave incorrect details about lock levels and
therefore incomplete reasons to use the option.

Initial bug report and fix from Marko Tiikkaja
Reworded by me to include comments by Kevin Grittner

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 5437626c3fe0e91dda236a9ba445d5630916f624..7ee0aa8ca0756675415a2a3b196188b776f276fc 100644 (file)
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -324,9 +324,13 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
       as <literal>NOT VALID</literal>, by scanning the table to ensure there
       are no rows for which the constraint is not satisfied.
       Nothing happens if the constraint is already marked valid.
-      The value of separating validation from initial creation of the
-      constraint is that validation requires a lesser lock on the table
-      than constraint creation does.
+     </para>
+     <para>
+      Validation can be a long process on larger tables and currently requires
+      an <literal>ACCESS EXCLUSIVE</literal> lock.  The value of separating
+      validation from initial creation is that you can defer validation to less
+      busy times, or can be used to give additional time to correct pre-existing
+      errors while preventing new errors.
      </para>
     </listitem>
    </varlistentry>