Remove overly-pessimistic statement about constraint exclusion.

As of 9.2, constraint exclusion should work okay with prepared statements:
the planner will try custom plans with actual values of the parameters,
and observe that they are a lot cheaper than the generic plan, and thus
never fall back to using the generic plan.  Noted by Tatsuhito Kasahara.

diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 013dc7c4dacdc56bbdfd001f6a0b615ecbead84b..07bfc203ec723c0fde82c56260e404842562660f 100644 (file)
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -2975,11 +2975,11 @@ ANALYZE measurement;
     
      
       Constraint exclusion only works when the query's WHERE
-      clause contains constants.  A parameterized query will not be
-      optimized, since the planner cannot know which partitions the
-      parameter value might select at run time.  For the same reason,
-      stable functions such as CURRENT_DATE
-      must be avoided.
+      clause contains constants (or externally supplied parameters).
+      For example, a comparison against a non-immutable function such as
+      CURRENT_TIMESTAMP cannot be optimized, since the
+      planner cannot know which partition the function value might fall
+      into at run time.