Restructure creation of run-time pruning steps.

Previously, gen_partprune_steps() always built executor pruning steps
using all suitable clauses, including those containing PARAM_EXEC
Params.  This meant that the pruning steps were only completely safe
for executor run-time (scan start) pruning.  To prune at executor
startup, we had to ignore the steps involving exec Params.  But this
doesn't really work in general, since there may be logic changes
needed as well --- for example, pruning according to the last operator's
btree strategy is the wrong thing if we're not applying that operator.
The rules embodied in gen_partprune_steps() and its minions are
sufficiently complicated that tracking their incremental effects in
other logic seems quite impractical.

Short of a complete redesign, the only safe fix seems to be to run
gen_partprune_steps() twice, once to create executor startup pruning
steps and then again for run-time pruning steps.  We can save a few
cycles however by noting during the first scan whether we rejected
any clauses because they involved exec Params --- if not, we don't
need to do the second scan.

In support of this, refactor the internal APIs in partprune.c to make
more use of passing information in the GeneratePruningStepsContext
struct, rather than as separate arguments.

This is, I hope, the last piece of our response to a bug report from
Alan Jackson.  Back-patch to v11 where this code came in.

Discussion: https://postgr.es/m/FAD28A83-AC73-489E-A058-2681FA31D648@tvsquared.com

1 files changed, 105 insertions, 75 deletions

diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
index 70709e5deab..6cdbb9db421 100644
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -183,6 +183,11 @@ static char *ExecBuildSlotPartitionKeyDescription(Relation rel,
 									 bool *isnull,
 									 int maxfieldlen);
 static List *adjust_partition_tlist(List *tlist, TupleConversionMap *map);
+static void ExecInitPruningContext(PartitionPruneContext *context,
+					   List *pruning_steps,
+					   PartitionDesc partdesc,
+					   PartitionKey partkey,
+					   PlanState *planstate);
 static void find_matching_subplans_recurse(PartitionPruningData *prunedata,
 							   PartitionedRelPruningData *pprune,
 							   bool initial_prune,
@@ -1614,16 +1619,9 @@ ExecCreatePartitionPruneState(PlanState *planstate,
 		{
 			PartitionedRelPruneInfo *pinfo = lfirst_node(PartitionedRelPruneInfo, lc2);
 			PartitionedRelPruningData *pprune = &prunedata->partrelprunedata[j];
-			PartitionPruneContext *context = &pprune->context;
 			Relation	partrel;
 			PartitionDesc partdesc;
 			PartitionKey partkey;
-			int			partnatts;
-			int			n_steps;
-			ListCell   *lc3;
-
-			/* present_parts is also subject to later modification */
-			pprune->present_parts = bms_copy(pinfo->present_parts);
 
 			/*
 			 * We can rely on the copies of the partitioned table's partition
@@ -1643,6 +1641,7 @@ ExecCreatePartitionPruneState(PlanState *planstate,
 			 * However, new partitions may have been added.
 			 */
 			Assert(partdesc->nparts >= pinfo->nparts);
+			pprune->nparts = partdesc->nparts;
 			pprune->subplan_map = palloc(sizeof(int) * partdesc->nparts);
 			if (partdesc->nparts == pinfo->nparts)
 			{
@@ -1700,66 +1699,30 @@ ExecCreatePartitionPruneState(PlanState *planstate,
 				Assert(pd_idx == pinfo->nparts);
 			}
 
-			n_steps = list_length(pinfo->pruning_steps);
-
-			context->strategy = partkey->strategy;
-			context->partnatts = partnatts = partkey->partnatts;
-			context->nparts = pinfo->nparts;
-			context->boundinfo = partdesc->boundinfo;
-			context->partcollation = partkey->partcollation;
-			context->partsupfunc = partkey->partsupfunc;
-
-			/* We'll look up type-specific support functions as needed */
-			context->stepcmpfuncs = (FmgrInfo *)
-				palloc0(sizeof(FmgrInfo) * n_steps * partnatts);
-
-			context->ppccontext = CurrentMemoryContext;
-			context->planstate = planstate;
+			/* present_parts is also subject to later modification */
+			pprune->present_parts = bms_copy(pinfo->present_parts);
 
-			/* Initialize expression state for each expression we need */
-			context->exprstates = (ExprState **)
-				palloc0(sizeof(ExprState *) * n_steps * partnatts);
-			foreach(lc3, pinfo->pruning_steps)
+			/*
+			 * Initialize pruning contexts as needed.
+			 */
+			pprune->initial_pruning_steps = pinfo->initial_pruning_steps;
+			if (pinfo->initial_pruning_steps)
 			{
-				PartitionPruneStepOp *step = (PartitionPruneStepOp *) lfirst(lc3);
-				ListCell   *lc4;
-				int			keyno;
-
-				/* not needed for other step kinds */
-				if (!IsA(step, PartitionPruneStepOp))
-					continue;
-
-				Assert(list_length(step->exprs) <= partnatts);
-
-				keyno = 0;
-				foreach(lc4, step->exprs)
-				{
-					Expr	   *expr = (Expr *) lfirst(lc4);
-
-					/* not needed for Consts */
-					if (!IsA(expr, Const))
-					{
-						int			stateidx = PruneCxtStateIdx(partnatts,
-																step->step.step_id,
-																keyno);
-
-						context->exprstates[stateidx] =
-							ExecInitExpr(expr, context->planstate);
-					}
-					keyno++;
-				}
+				ExecInitPruningContext(&pprune->initial_context,
+									   pinfo->initial_pruning_steps,
+									   partdesc, partkey, planstate);
+				/* Record whether initial pruning is needed at any level */
+				prunestate->do_initial_prune = true;
+			}
+			pprune->exec_pruning_steps = pinfo->exec_pruning_steps;
+			if (pinfo->exec_pruning_steps)
+			{
+				ExecInitPruningContext(&pprune->exec_context,
+									   pinfo->exec_pruning_steps,
+									   partdesc, partkey, planstate);
+				/* Record whether exec pruning is needed at any level */
+				prunestate->do_exec_prune = true;
 			}
-
-			/* Array is not modified at runtime, so just point to plan's copy */
-			context->exprhasexecparam = pinfo->hasexecparam;
-
-			pprune->pruning_steps = pinfo->pruning_steps;
-			pprune->do_initial_prune = pinfo->do_initial_prune;
-			pprune->do_exec_prune = pinfo->do_exec_prune;
-
-			/* Record if pruning would be useful at any level */
-			prunestate->do_initial_prune |= pinfo->do_initial_prune;
-			prunestate->do_exec_prune |= pinfo->do_exec_prune;
 
 			/*
 			 * Accumulate the IDs of all PARAM_EXEC Params affecting the
@@ -1777,6 +1740,71 @@ ExecCreatePartitionPruneState(PlanState *planstate,
 }
 
 /*
+ * Initialize a PartitionPruneContext for the given list of pruning steps.
+ */
+static void
+ExecInitPruningContext(PartitionPruneContext *context,
+					   List *pruning_steps,
+					   PartitionDesc partdesc,
+					   PartitionKey partkey,
+					   PlanState *planstate)
+{
+	int			n_steps;
+	int			partnatts;
+	ListCell   *lc;
+
+	n_steps = list_length(pruning_steps);
+
+	context->strategy = partkey->strategy;
+	context->partnatts = partnatts = partkey->partnatts;
+	context->nparts = partdesc->nparts;
+	context->boundinfo = partdesc->boundinfo;
+	context->partcollation = partkey->partcollation;
+	context->partsupfunc = partkey->partsupfunc;
+
+	/* We'll look up type-specific support functions as needed */
+	context->stepcmpfuncs = (FmgrInfo *)
+		palloc0(sizeof(FmgrInfo) * n_steps * partnatts);
+
+	context->ppccontext = CurrentMemoryContext;
+	context->planstate = planstate;
+
+	/* Initialize expression state for each expression we need */
+	context->exprstates = (ExprState **)
+		palloc0(sizeof(ExprState *) * n_steps * partnatts);
+	foreach(lc, pruning_steps)
+	{
+		PartitionPruneStepOp *step = (PartitionPruneStepOp *) lfirst(lc);
+		ListCell   *lc2;
+		int			keyno;
+
+		/* not needed for other step kinds */
+		if (!IsA(step, PartitionPruneStepOp))
+			continue;
+
+		Assert(list_length(step->exprs) <= partnatts);
+
+		keyno = 0;
+		foreach(lc2, step->exprs)
+		{
+			Expr	   *expr = (Expr *) lfirst(lc2);
+
+			/* not needed for Consts */
+			if (!IsA(expr, Const))
+			{
+				int			stateidx = PruneCxtStateIdx(partnatts,
+														step->step.step_id,
+														keyno);
+
+				context->exprstates[stateidx] =
+					ExecInitExpr(expr, context->planstate);
+			}
+			keyno++;
+		}
+	}
+}
+
+/*
  * ExecFindInitialMatchingSubPlans
  *		Identify the set of subplans that cannot be eliminated by initial
  *		pruning, disregarding any pruning constraints involving PARAM_EXEC
@@ -1824,7 +1852,8 @@ ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubplans)
 		find_matching_subplans_recurse(prunedata, pprune, true, &result);
 
 		/* Expression eval may have used space in node's ps_ExprContext too */
-		ResetExprContext(pprune->context.planstate->ps_ExprContext);
+		if (pprune->initial_pruning_steps)
+			ResetExprContext(pprune->initial_context.planstate->ps_ExprContext);
 	}
 
 	/* Add in any subplans that partition pruning didn't account for */
@@ -1888,7 +1917,7 @@ ExecFindInitialMatchingSubPlans(PartitionPruneState *prunestate, int nsubplans)
 			for (j = prunedata->num_partrelprunedata - 1; j >= 0; j--)
 			{
 				PartitionedRelPruningData *pprune = &prunedata->partrelprunedata[j];
-				int			nparts = pprune->context.nparts;
+				int			nparts = pprune->nparts;
 				int			k;
 
 				/* We just rebuild present_parts from scratch */
@@ -1993,7 +2022,8 @@ ExecFindMatchingSubPlans(PartitionPruneState *prunestate)
 		find_matching_subplans_recurse(prunedata, pprune, false, &result);
 
 		/* Expression eval may have used space in node's ps_ExprContext too */
-		ResetExprContext(pprune->context.planstate->ps_ExprContext);
+		if (pprune->exec_pruning_steps)
+			ResetExprContext(pprune->exec_context.planstate->ps_ExprContext);
 	}
 
 	/* Add in any subplans that partition pruning didn't account for */
@@ -2029,15 +2059,15 @@ find_matching_subplans_recurse(PartitionPruningData *prunedata,
 	check_stack_depth();
 
 	/* Only prune if pruning would be useful at this level. */
-	if (initial_prune ? pprune->do_initial_prune : pprune->do_exec_prune)
+	if (initial_prune && pprune->initial_pruning_steps)
 	{
-		PartitionPruneContext *context = &pprune->context;
-
-		/* Set whether we can evaluate PARAM_EXEC Params or not */
-		context->evalexecparams = !initial_prune;
-
-		partset = get_matching_partitions(context,
-										  pprune->pruning_steps);
+		partset = get_matching_partitions(&pprune->initial_context,
+										  pprune->initial_pruning_steps);
+	}
+	else if (!initial_prune && pprune->exec_pruning_steps)
+	{
+		partset = get_matching_partitions(&pprune->exec_context,
+										  pprune->exec_pruning_steps);
 	}
 	else
 	{