Expression evaluation based aggregate transition invocation.

Previously aggregate transition and combination functions were invoked
by special case code in nodeAgg.c, evaluating input and filters
separately using the expression evaluation machinery. That turns out
to not be great for performance for several reasons:

- repeated expression evaluations have some cost
- the transition functions invocations are poorly predicted, as
  commonly there are multiple aggregates in a query, resulting in the
  same call-stack invoking different functions.
- filter and input computation had to be done separately
- the special case code made it hard to implement JITing of the whole
  transition function invocation

Address this by building one large expression that computes input,
evaluates filters, and invokes transition functions.

This leads to moderate speedups in queries bottlenecked by aggregate
computations, and enables large speedups for similar cases once JITing
is done.

There's potential for further improvement:
- It'd be nice if we could simplify the somewhat expensive
  aggstate->all_pergroups lookups.
- right now there's still an advance_transition_function invocation in
  nodeAgg.c, leading to some code duplication.

Author: Andres Freund
Discussion: https://postgr.es/m/20170901064131.tazjxwus3k2w3ybh@alap3.anarazel.de

1 files changed, 3 insertions, 1 deletions

diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
index a782fae0f83..6545a802223 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -192,7 +192,7 @@ extern void ExecConstraints(ResultRelInfo *resultRelInfo,
 extern bool ExecPartitionCheck(ResultRelInfo *resultRelInfo,
 				   TupleTableSlot *slot, EState *estate);
 extern void ExecPartitionCheckEmitError(ResultRelInfo *resultRelInfo,
-									TupleTableSlot *slot, EState *estate);
+							TupleTableSlot *slot, EState *estate);
 extern void ExecWithCheckOptions(WCOKind kind, ResultRelInfo *resultRelInfo,
 					 TupleTableSlot *slot, EState *estate);
 extern LockTupleMode ExecUpdateLockMode(EState *estate, ResultRelInfo *relinfo);
@@ -254,6 +254,8 @@ extern ExprState *ExecInitExprWithParams(Expr *node, ParamListInfo ext_params);
 extern ExprState *ExecInitQual(List *qual, PlanState *parent);
 extern ExprState *ExecInitCheck(List *qual, PlanState *parent);
 extern List *ExecInitExprList(List *nodes, PlanState *parent);
+extern ExprState *ExecBuildAggTrans(AggState *aggstate, struct AggStatePerPhaseData *phase,
+				  bool doSort, bool doHash);
 extern ProjectionInfo *ExecBuildProjectionInfo(List *targetList,
 						ExprContext *econtext,
 						TupleTableSlot *slot,