Fix runtime partition pruning for HASH partitioned tables

This could only affect HASH partitioned tables with at least 2 partition
key columns.

If partition pruning was delayed until execution and the query contained
an IS NULL qual on one of the partitioned keys, and some subsequent
partitioned key was being compared to a non-Const, then this could result
in a crash due to the incorrect keyno being used to calculate the
stateidx for the expression evaluation code.

Here we fix this by properly skipping partitioned keys which have a
nullkey set.  Effectively, this must be the same as what's going on
inside perform_pruning_base_step().

Sergei Glukhov also provided a patch, but that's not what's being used
here.

Reported-by: Sergei Glukhov
Reviewed-by: tender wang, Sergei Glukhov
Discussion: https://postgr.es/m/d05b26fa-af54-27e1-f693-6c31590802fa@postgrespro.ru
Backpatch-through: 11, where runtime partition pruning was added.

1 files changed, 29 insertions, 24 deletions

diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
index 73bc5bb9585..ba5a58d027c 100644
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -1956,7 +1956,7 @@ InitPartitionPruneContext(PartitionPruneContext *context,
 	foreach(lc, pruning_steps)
 	{
 		PartitionPruneStepOp *step = (PartitionPruneStepOp *) lfirst(lc);
-		ListCell   *lc2;
+		ListCell   *lc2 = list_head(step->exprs);
 		int			keyno;
 
 		/* not needed for other step kinds */
@@ -1965,34 +1965,39 @@ InitPartitionPruneContext(PartitionPruneContext *context,
 
 		Assert(list_length(step->exprs) <= partnatts);
 
-		keyno = 0;
-		foreach(lc2, step->exprs)
+		for (keyno = 0; keyno < partnatts; keyno++)
 		{
-			Expr	   *expr = (Expr *) lfirst(lc2);
+			if (bms_is_member(keyno, step->nullkeys))
+				continue;
 
-			/* not needed for Consts */
-			if (!IsA(expr, Const))
+			if (lc2 != NULL)
 			{
-				int			stateidx = PruneCxtStateIdx(partnatts,
-														step->step.step_id,
-														keyno);
+				Expr	   *expr = lfirst(lc2);
 
-				/*
-				 * When planstate is NULL, pruning_steps is known not to
-				 * contain any expressions that depend on the parent plan.
-				 * Information of any available EXTERN parameters must be
-				 * passed explicitly in that case, which the caller must have
-				 * made available via econtext.
-				 */
-				if (planstate == NULL)
-					context->exprstates[stateidx] =
-						ExecInitExprWithParams(expr,
-											   econtext->ecxt_param_list_info);
-				else
-					context->exprstates[stateidx] =
-						ExecInitExpr(expr, context->planstate);
+				/* not needed for Consts */
+				if (!IsA(expr, Const))
+				{
+					int			stateidx = PruneCxtStateIdx(partnatts,
+															step->step.step_id,
+															keyno);
+
+					/*
+					 * When planstate is NULL, pruning_steps is known not to
+					 * contain any expressions that depend on the parent plan.
+					 * Information of any available EXTERN parameters must be
+					 * passed explicitly in that case, which the caller must
+					 * have made available via econtext.
+					 */
+					if (planstate == NULL)
+						context->exprstates[stateidx] =
+							ExecInitExprWithParams(expr,
+												   econtext->ecxt_param_list_info);
+					else
+						context->exprstates[stateidx] =
+							ExecInitExpr(expr, context->planstate);
+				}
+				lc2 = lnext(step->exprs, lc2);
 			}
-			keyno++;
 		}
 	}
 }