Share transition state between different aggregates when possible.

If there are two different aggregates in the query with same inputs, and
the aggregates have the same initial condition and transition function,
only calculate the state value once, and only call the final functions
separately. For example, AVG(x) and SUM(x) aggregates have the same
transition function, which accumulates the sum and number of input tuples.
For a query like "SELECT AVG(x), SUM(x) FROM x", we can therefore
accumulate the state function only once, which gives a nice speedup.

David Rowley, reviewed and edited by me.

2 files changed, 13 insertions, 9 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 303fc3c1c77..5796de861c4 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -609,9 +609,6 @@ typedef struct WholeRowVarExprState
 typedef struct AggrefExprState
 {
 	ExprState	xprstate;
-	List	   *aggdirectargs;	/* states of direct-argument expressions */
-	List	   *args;			/* states of aggregated-argument expressions */
-	ExprState  *aggfilter;		/* state of FILTER expression, if any */
 	int			aggno;			/* ID number for agg within its plan node */
 } AggrefExprState;
 
@@ -1825,6 +1822,7 @@ typedef struct GroupState
  */
 /* these structs are private in nodeAgg.c: */
 typedef struct AggStatePerAggData *AggStatePerAgg;
+typedef struct AggStatePerTransData *AggStatePerTrans;
 typedef struct AggStatePerGroupData *AggStatePerGroup;
 typedef struct AggStatePerPhaseData *AggStatePerPhase;
 
@@ -1833,14 +1831,16 @@ typedef struct AggState
 	ScanState	ss;				/* its first field is NodeTag */
 	List	   *aggs;			/* all Aggref nodes in targetlist & quals */
 	int			numaggs;		/* length of list (could be zero!) */
+	int			numtrans;		/* number of pertrans items */
 	AggStatePerPhase phase;		/* pointer to current phase data */
 	int			numphases;		/* number of phases */
 	int			current_phase;	/* current phase number */
 	FmgrInfo   *hashfunctions;	/* per-grouping-field hash fns */
 	AggStatePerAgg peragg;		/* per-Aggref information */
+	AggStatePerTrans pertrans;	/* per-Trans state information */
 	ExprContext **aggcontexts;	/* econtexts for long-lived data (per GS) */
 	ExprContext *tmpcontext;	/* econtext for input expressions */
-	AggStatePerAgg curperagg;	/* identifies currently active aggregate */
+	AggStatePerTrans curpertrans;	/* currently active trans state */
 	bool		input_done;		/* indicates end of input */
 	bool		agg_done;		/* indicates completion of Agg scan */
 	int			projected_set;	/* The last projected grouping set */
diff --git a/src/include/parser/parse_agg.h b/src/include/parser/parse_agg.h
index 6a5f9bbdf15..e2b3894c282 100644
--- a/src/include/parser/parse_agg.h
+++ b/src/include/parser/parse_agg.h
@@ -35,19 +35,23 @@ extern Oid resolve_aggregate_transtype(Oid aggfuncid,
 							Oid *inputTypes,
 							int numArguments);
 
-extern void build_aggregate_fnexprs(Oid *agg_input_types,
+extern void build_aggregate_transfn_expr(Oid *agg_input_types,
 						int agg_num_inputs,
 						int agg_num_direct_inputs,
-						int num_finalfn_inputs,
 						bool agg_variadic,
 						Oid agg_state_type,
-						Oid agg_result_type,
 						Oid agg_input_collation,
 						Oid transfn_oid,
 						Oid invtransfn_oid,
-						Oid finalfn_oid,
 						Expr **transfnexpr,
-						Expr **invtransfnexpr,
+						Expr **invtransfnexpr);
+
+extern void build_aggregate_finalfn_expr(Oid *agg_input_types,
+						int num_finalfn_inputs,
+						Oid agg_state_type,
+						Oid agg_result_type,
+						Oid agg_input_collation,
+						Oid finalfn_oid,
 						Expr **finalfnexpr);
 
 #endif   /* PARSE_AGG_H */