Support MergeAppend plans, to allow sorted output from append relations.

This patch eliminates the former need to sort the output of an Append scan
when an ordered scan of an inheritance tree is wanted.  This should be
particularly useful for fast-start cases such as queries with LIMIT.

Original patch by Greg Stark, with further hacking by Hans-Jurgen Schonig,
Robert Haas, and Tom Lane.

1 files changed, 23 insertions, 0 deletions

diff --git a/src/backend/executor/execCurrent.c b/src/backend/executor/execCurrent.c
index 79a1425a974..cf552a016a5 100644
--- a/src/backend/executor/execCurrent.c
+++ b/src/backend/executor/execCurrent.c
@@ -296,6 +296,29 @@ search_plan_tree(PlanState *node, Oid table_oid)
 			}
 
 			/*
+			 * Similarly for MergeAppend
+			 */
+		case T_MergeAppendState:
+			{
+				MergeAppendState *mstate = (MergeAppendState *) node;
+				ScanState  *result = NULL;
+				int			i;
+
+				for (i = 0; i < mstate->ms_nplans; i++)
+				{
+					ScanState  *elem = search_plan_tree(mstate->mergeplans[i],
+														table_oid);
+
+					if (!elem)
+						continue;
+					if (result)
+						return NULL;	/* multiple matches */
+					result = elem;
+				}
+				return result;
+			}
+
+			/*
 			 * Result and Limit can be descended through (these are safe
 			 * because they always return their input's current row)
 			 */