From 2759924f33a6b7021f68dda05bb34b10bb4579e2 Mon Sep 17 00:00:00 2001
From: David Rowley <drowley@postgresql.org>
Date: Fri, 13 Oct 2023 01:15:12 +1300
Subject: [PATCH] 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.
---
 src/backend/executor/execPartition.c | 29 ++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/src/backend/executor/execPartition.c b/src/backend/executor/execPartition.c
index b667d03c7f..d4c6833650 100644
--- a/src/backend/executor/execPartition.c
+++ b/src/backend/executor/execPartition.c
@@ -1673,7 +1673,7 @@ ExecInitPruningContext(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 */
@@ -1682,22 +1682,27 @@ ExecInitPruningContext(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);
 
-				context->exprstates[stateidx] =
-					ExecInitExpr(expr, context->planstate);
+				/* not needed for Consts */
+				if (!IsA(expr, Const))
+				{
+					int			stateidx = PruneCxtStateIdx(partnatts,
+															step->step.step_id,
+															keyno);
+
+					context->exprstates[stateidx] =
+						ExecInitExpr(expr, context->planstate);
+				}
+				lc2 = lnext(lc2);
 			}
-			keyno++;
 		}
 	}
 }