Faster expression evaluation and targetlist projection.

This replaces the old, recursive tree-walk based evaluation, with
non-recursive, opcode dispatch based, expression evaluation.
Projection is now implemented as part of expression evaluation.

This both leads to significant performance improvements, and makes
future just-in-time compilation of expressions easier.

The speed gains primarily come from:
- non-recursive implementation reduces stack usage / overhead
- simple sub-expressions are implemented with a single jump, without
  function calls
- sharing some state between different sub-expressions
- reduced amount of indirect/hard to predict memory accesses by laying
  out operation metadata sequentially; including the avoidance of
  nearly all of the previously used linked lists
- more code has been moved to expression initialization, avoiding
  constant re-checks at evaluation time

Future just-in-time compilation (JIT) has become easier, as
demonstrated by released patches intended to be merged in a later
release, for primarily two reasons: Firstly, due to a stricter split
between expression initialization and evaluation, less code has to be
handled by the JIT. Secondly, due to the non-recursive nature of the
generated "instructions", less performance-critical code-paths can
easily be shared between interpreted and compiled evaluation.

The new framework allows for significant future optimizations. E.g.:
- basic infrastructure for to later reduce the per executor-startup
  overhead of expression evaluation, by caching state in prepared
  statements.  That'd be helpful in OLTPish scenarios where
  initialization overhead is measurable.
- optimizing the generated "code". A number of proposals for potential
  work has already been made.
- optimizing the interpreter. Similarly a number of proposals have
  been made here too.

The move of logic into the expression initialization step leads to some
backward-incompatible changes:
- Function permission checks are now done during expression
  initialization, whereas previously they were done during
  execution. In edge cases this can lead to errors being raised that
  previously wouldn't have been, e.g. a NULL array being coerced to a
  different array type previously didn't perform checks.
- The set of domain constraints to be checked, is now evaluated once
  during expression initialization, previously it was re-built
  every time a domain check was evaluated. For normal queries this
  doesn't change much, but e.g. for plpgsql functions, which caches
  ExprStates, the old set could stick around longer.  The behavior
  around might still change.

Author: Andres Freund, with significant changes by Tom Lane,
	changes by Heikki Linnakangas
Reviewed-By: Tom Lane, Heikki Linnakangas
Discussion: https://postgr.es/m/20161206034955.bh33paeralxbtluv@alap3.anarazel.de

1 files changed, 39 insertions, 57 deletions

diff --git a/src/backend/executor/nodeSubplan.c b/src/backend/executor/nodeSubplan.c
index 8f419a13acd..b3a025879a1 100644
--- a/src/backend/executor/nodeSubplan.c
+++ b/src/backend/executor/nodeSubplan.c
@@ -39,12 +39,6 @@
 #include "utils/memutils.h"
 
 
-static Datum ExecSubPlan(SubPlanState *node,
-			ExprContext *econtext,
-			bool *isNull);
-static Datum ExecAlternativeSubPlan(AlternativeSubPlanState *node,
-					   ExprContext *econtext,
-					   bool *isNull);
 static Datum ExecHashSubPlan(SubPlanState *node,
 				ExprContext *econtext,
 				bool *isNull);
@@ -64,12 +58,12 @@ static bool slotNoNulls(TupleTableSlot *slot);
  * This is the main entry point for execution of a regular SubPlan.
  * ----------------------------------------------------------------
  */
-static Datum
+Datum
 ExecSubPlan(SubPlanState *node,
 			ExprContext *econtext,
 			bool *isNull)
 {
-	SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
+	SubPlan    *subplan = node->subplan;
 
 	/* Set non-null as default */
 	*isNull = false;
@@ -95,7 +89,7 @@ ExecHashSubPlan(SubPlanState *node,
 				ExprContext *econtext,
 				bool *isNull)
 {
-	SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
+	SubPlan    *subplan = node->subplan;
 	PlanState  *planstate = node->planstate;
 	TupleTableSlot *slot;
 
@@ -217,7 +211,7 @@ ExecScanSubPlan(SubPlanState *node,
 				ExprContext *econtext,
 				bool *isNull)
 {
-	SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
+	SubPlan    *subplan = node->subplan;
 	PlanState  *planstate = node->planstate;
 	SubLinkType subLinkType = subplan->subLinkType;
 	MemoryContext oldcontext;
@@ -462,7 +456,7 @@ ExecScanSubPlan(SubPlanState *node,
 static void
 buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
 {
-	SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
+	SubPlan    *subplan = node->subplan;
 	PlanState  *planstate = node->planstate;
 	int			ncols = list_length(subplan->paramIds);
 	ExprContext *innerecontext = node->innerecontext;
@@ -596,7 +590,7 @@ buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
 	 * potential for a double free attempt.  (XXX possibly no longer needed,
 	 * but can't hurt.)
 	 */
-	ExecClearTuple(node->projRight->pi_slot);
+	ExecClearTuple(node->projRight->pi_state.resultslot);
 
 	MemoryContextSwitchTo(oldcontext);
 }
@@ -694,8 +688,7 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 	SubPlanState *sstate = makeNode(SubPlanState);
 	EState	   *estate = parent->state;
 
-	sstate->xprstate.evalfunc = (ExprStateEvalFunc) ExecSubPlan;
-	sstate->xprstate.expr = (Expr *) subplan;
+	sstate->subplan = subplan;
 
 	/* Link the SubPlanState to already-initialized subplan */
 	sstate->planstate = (PlanState *) list_nth(estate->es_subplanstates,
@@ -706,7 +699,7 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 
 	/* Initialize subexpressions */
 	sstate->testexpr = ExecInitExpr((Expr *) subplan->testexpr, parent);
-	sstate->args = (List *) ExecInitExpr((Expr *) subplan->args, parent);
+	sstate->args = ExecInitExprList(subplan->args, parent);
 
 	/*
 	 * initialize my state
@@ -763,9 +756,7 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 		TupleTableSlot *slot;
 		List	   *oplist,
 				   *lefttlist,
-				   *righttlist,
-				   *leftptlist,
-				   *rightptlist;
+				   *righttlist;
 		ListCell   *l;
 
 		/* We need a memory context to hold the hash table(s) */
@@ -792,35 +783,33 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 		 * use the sub-select's output tuples directly, but that is not the
 		 * case if we had to insert any run-time coercions of the sub-select's
 		 * output datatypes; anyway this avoids storing any resjunk columns
-		 * that might be in the sub-select's output.) Run through the
+		 * that might be in the sub-select's output.)  Run through the
 		 * combining expressions to build tlists for the lefthand and
-		 * righthand sides.  We need both the ExprState list (for ExecProject)
-		 * and the underlying parse Exprs (for ExecTypeFromTL).
+		 * righthand sides.
 		 *
 		 * We also extract the combining operators themselves to initialize
 		 * the equality and hashing functions for the hash tables.
 		 */
-		if (IsA(sstate->testexpr->expr, OpExpr))
+		if (IsA(subplan->testexpr, OpExpr))
 		{
 			/* single combining operator */
-			oplist = list_make1(sstate->testexpr);
+			oplist = list_make1(subplan->testexpr);
 		}
-		else if (and_clause((Node *) sstate->testexpr->expr))
+		else if (and_clause((Node *) subplan->testexpr))
 		{
 			/* multiple combining operators */
-			oplist = castNode(BoolExprState, sstate->testexpr)->args;
+			oplist = castNode(BoolExpr, subplan->testexpr)->args;
 		}
 		else
 		{
 			/* shouldn't see anything else in a hashable subplan */
 			elog(ERROR, "unrecognized testexpr type: %d",
-				 (int) nodeTag(sstate->testexpr->expr));
+				 (int) nodeTag(subplan->testexpr));
 			oplist = NIL;		/* keep compiler quiet */
 		}
 		Assert(list_length(oplist) == ncols);
 
 		lefttlist = righttlist = NIL;
-		leftptlist = rightptlist = NIL;
 		sstate->tab_hash_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
 		sstate->tab_eq_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
 		sstate->lhs_hash_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
@@ -828,45 +817,30 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 		i = 1;
 		foreach(l, oplist)
 		{
-			FuncExprState *fstate = castNode(FuncExprState, lfirst(l));
-			OpExpr	   *opexpr = castNode(OpExpr, fstate->xprstate.expr);
-			ExprState  *exstate;
+			OpExpr	   *opexpr = castNode(OpExpr, lfirst(l));
 			Expr	   *expr;
 			TargetEntry *tle;
-			GenericExprState *tlestate;
 			Oid			rhs_eq_oper;
 			Oid			left_hashfn;
 			Oid			right_hashfn;
 
-			Assert(list_length(fstate->args) == 2);
+			Assert(list_length(opexpr->args) == 2);
 
 			/* Process lefthand argument */
-			exstate = (ExprState *) linitial(fstate->args);
-			expr = exstate->expr;
+			expr = (Expr *) linitial(opexpr->args);
 			tle = makeTargetEntry(expr,
 								  i,
 								  NULL,
 								  false);
-			tlestate = makeNode(GenericExprState);
-			tlestate->xprstate.expr = (Expr *) tle;
-			tlestate->xprstate.evalfunc = NULL;
-			tlestate->arg = exstate;
-			lefttlist = lappend(lefttlist, tlestate);
-			leftptlist = lappend(leftptlist, tle);
+			lefttlist = lappend(lefttlist, tle);
 
 			/* Process righthand argument */
-			exstate = (ExprState *) lsecond(fstate->args);
-			expr = exstate->expr;
+			expr = (Expr *) lsecond(opexpr->args);
 			tle = makeTargetEntry(expr,
 								  i,
 								  NULL,
 								  false);
-			tlestate = makeNode(GenericExprState);
-			tlestate->xprstate.expr = (Expr *) tle;
-			tlestate->xprstate.evalfunc = NULL;
-			tlestate->arg = exstate;
-			righttlist = lappend(righttlist, tlestate);
-			rightptlist = lappend(rightptlist, tle);
+			righttlist = lappend(righttlist, tle);
 
 			/* Lookup the equality function (potentially cross-type) */
 			fmgr_info(opexpr->opfuncid, &sstate->cur_eq_funcs[i - 1]);
@@ -898,20 +872,22 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 		 * (hack alert!).  The righthand expressions will be evaluated in our
 		 * own innerecontext.
 		 */
-		tupDesc = ExecTypeFromTL(leftptlist, false);
+		tupDesc = ExecTypeFromTL(lefttlist, false);
 		slot = ExecInitExtraTupleSlot(estate);
 		ExecSetSlotDescriptor(slot, tupDesc);
 		sstate->projLeft = ExecBuildProjectionInfo(lefttlist,
 												   NULL,
 												   slot,
+												   parent,
 												   NULL);
 
-		tupDesc = ExecTypeFromTL(rightptlist, false);
+		tupDesc = ExecTypeFromTL(righttlist, false);
 		slot = ExecInitExtraTupleSlot(estate);
 		ExecSetSlotDescriptor(slot, tupDesc);
 		sstate->projRight = ExecBuildProjectionInfo(righttlist,
 													sstate->innerecontext,
 													slot,
+													sstate->planstate,
 													NULL);
 	}
 
@@ -934,7 +910,7 @@ ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
 void
 ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
 {
-	SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
+	SubPlan    *subplan = node->subplan;
 	PlanState  *planstate = node->planstate;
 	SubLinkType subLinkType = subplan->subLinkType;
 	MemoryContext oldcontext;
@@ -1111,7 +1087,7 @@ void
 ExecReScanSetParamPlan(SubPlanState *node, PlanState *parent)
 {
 	PlanState  *planstate = node->planstate;
-	SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
+	SubPlan    *subplan = node->subplan;
 	EState	   *estate = parent->state;
 	ListCell   *l;
 
@@ -1162,16 +1138,22 @@ ExecInitAlternativeSubPlan(AlternativeSubPlan *asplan, PlanState *parent)
 	SubPlan    *subplan2;
 	Cost		cost1;
 	Cost		cost2;
+	ListCell   *lc;
 
-	asstate->xprstate.evalfunc = (ExprStateEvalFunc) ExecAlternativeSubPlan;
-	asstate->xprstate.expr = (Expr *) asplan;
+	asstate->subplan = asplan;
 
 	/*
 	 * Initialize subplans.  (Can we get away with only initializing the one
 	 * we're going to use?)
 	 */
-	asstate->subplans = (List *) ExecInitExpr((Expr *) asplan->subplans,
-											  parent);
+	foreach(lc, asplan->subplans)
+	{
+		SubPlan    *sp = castNode(SubPlan, lfirst(lc));
+		SubPlanState *sps = ExecInitSubPlan(sp, parent);
+
+		asstate->subplans = lappend(asstate->subplans, sps);
+		parent->subPlan = lappend(parent->subPlan, sps);
+	}
 
 	/*
 	 * Select the one to be used.  For this, we need an estimate of the number
@@ -1209,7 +1191,7 @@ ExecInitAlternativeSubPlan(AlternativeSubPlan *asplan, PlanState *parent)
  * Note: in future we might consider changing to different subplans on the
  * fly, in case the original rowcount estimate turns out to be way off.
  */
-static Datum
+Datum
 ExecAlternativeSubPlan(AlternativeSubPlanState *node,
 					   ExprContext *econtext,
 					   bool *isNull)