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.

1 files changed, 39 insertions, 0 deletions

diff --git a/src/backend/parser/parse_agg.c b/src/backend/parser/parse_agg.c
index 583462a9181..91bfe66c590 100644
--- a/src/backend/parser/parse_agg.c
+++ b/src/backend/parser/parse_agg.c
@@ -1966,6 +1966,45 @@ build_aggregate_combinefn_expr(Oid agg_state_type,
 
 /*
  * Like build_aggregate_transfn_expr, but creates an expression tree for the
+ * serialization or deserialization function of an aggregate, rather than the
+ * transition function. This may be used for either the serialization or
+ * deserialization function by swapping the first two parameters over.
+ */
+void
+build_aggregate_serialfn_expr(Oid agg_input_type,
+							  Oid agg_output_type,
+							  Oid agg_input_collation,
+							  Oid serialfn_oid,
+							  Expr **serialfnexpr)
+{
+	Param	   *argp;
+	List	   *args;
+	FuncExpr   *fexpr;
+
+	/* Build arg list to use in the FuncExpr node. */
+	argp = makeNode(Param);
+	argp->paramkind = PARAM_EXEC;
+	argp->paramid = -1;
+	argp->paramtype = agg_input_type;
+	argp->paramtypmod = -1;
+	argp->paramcollid = agg_input_collation;
+	argp->location = -1;
+
+	/* takes a single arg of the agg_input_type */
+	args = list_make1(argp);
+
+	fexpr = makeFuncExpr(serialfn_oid,
+						 agg_output_type,
+						 args,
+						 InvalidOid,
+						 agg_input_collation,
+						 COERCE_EXPLICIT_CALL);
+	fexpr->funcvariadic = false;
+	*serialfnexpr = (Expr *) fexpr;
+}
+
+/*
+ * Like build_aggregate_transfn_expr, but creates an expression tree for the
  * final function of an aggregate, rather than the transition function.
  */
 void