Allow aggregate transition states to be serialized and deserialized.

This is necessary infrastructure for supporting parallel aggregation
for aggregates whose transition type is "internal".  Such values
can't be passed between cooperating processes, because they are
just pointers.

David Rowley, reviewed by Tomas Vondra and by me.

3 files changed, 19 insertions, 8 deletions

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index d80dfbe5c9f..c615717dea3 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -464,11 +464,15 @@ aggregates_allow_partial_walker(Node *node, partial_agg_context *context)
 		}
 
 		/*
-		 * If we find any aggs with an internal transtype then we must ensure
-		 * that pointers to aggregate states are not passed to other processes;
-		 * therefore, we set the maximum allowed type to PAT_INTERNAL_ONLY.
+		 * If we find any aggs with an internal transtype then we must check
+		 * that these have a serialization type, serialization func and
+		 * deserialization func; otherwise, we set the maximum allowed type to
+		 * PAT_INTERNAL_ONLY.
 		 */
-		if (aggform->aggtranstype == INTERNALOID)
+		if (aggform->aggtranstype == INTERNALOID &&
+			(!OidIsValid(aggform->aggserialtype) ||
+			 !OidIsValid(aggform->aggserialfn) ||
+			 !OidIsValid(aggform->aggdeserialfn)))
 			context->allowedtype = PAT_INTERNAL_ONLY;
 
 		ReleaseSysCache(aggTuple);
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index 16b34fcf46a..89cae793ca3 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -2433,7 +2433,8 @@ create_agg_path(PlannerInfo *root,
 				const AggClauseCosts *aggcosts,
 				double numGroups,
 				bool combineStates,
-				bool finalizeAggs)
+				bool finalizeAggs,
+				bool serialStates)
 {
 	AggPath    *pathnode = makeNode(AggPath);
 
@@ -2458,6 +2459,7 @@ create_agg_path(PlannerInfo *root,
 	pathnode->qual = qual;
 	pathnode->finalizeAggs = finalizeAggs;
 	pathnode->combineStates = combineStates;
+	pathnode->serialStates = serialStates;
 
 	cost_agg(&pathnode->path, root,
 			 aggstrategy, aggcosts,
diff --git a/src/backend/optimizer/util/tlist.c b/src/backend/optimizer/util/tlist.c
index cd421b14632..4c8c83da80d 100644
--- a/src/backend/optimizer/util/tlist.c
+++ b/src/backend/optimizer/util/tlist.c
@@ -756,8 +756,8 @@ apply_pathtarget_labeling_to_tlist(List *tlist, PathTarget *target)
  * apply_partialaggref_adjustment
  *	  Convert PathTarget to be suitable for a partial aggregate node. We simply
  *	  adjust any Aggref nodes found in the target and set the aggoutputtype to
- *	  the aggtranstype. This allows exprType() to return the actual type that
- *	  will be produced.
+ *	  the aggtranstype or aggserialtype. This allows exprType() to return the
+ *	  actual type that will be produced.
  *
  * Note: We expect 'target' to be a flat target list and not have Aggrefs burried
  * within other expressions.
@@ -785,7 +785,12 @@ apply_partialaggref_adjustment(PathTarget *target)
 			aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);
 
 			newaggref = (Aggref *) copyObject(aggref);
-			newaggref->aggoutputtype = aggform->aggtranstype;
+
+			/* use the serialization type, if one exists */
+			if (OidIsValid(aggform->aggserialtype))
+				newaggref->aggoutputtype = aggform->aggserialtype;
+			else
+				newaggref->aggoutputtype = aggform->aggtranstype;
 
 			lfirst(lc) = newaggref;