Don't rely on uninitialized value in MERGE / DELETE

alvherre · alvherre · commit fd923b5de94c · 2023-02-15T20:37:44.000+01:00
On MERGE / WHEN MATCHED DELETE it's not possible to get cross-partition updates, so we don't initialize cpUpdateRetrySlot; however, the code was not careful to ignore the value in that case. Make it do so. Backpatch to 15. Reported-by: Alexander Lakhin <exclusion@gmail.com> Reviewed-by: Dean Rasheed <dean.a.rasheed@gmail.com> Discussion: https://postgr.es/m/17792-0f89452029662c36@postgresql.org
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
@@ -2967,21 +2967,20 @@ ExecMergeMatched(ModifyTableContext *context, ResultRelInfo *resultRelInfo,
 					 */
 
 					/*
-					 * If cpUpdateRetrySlot is set, ExecCrossPartitionUpdate()
-					 * must have detected that the tuple was concurrently
-					 * updated, so we restart the search for an appropriate
-					 * WHEN MATCHED clause to process the updated tuple.
+					 * During an UPDATE, if cpUpdateRetrySlot is set, then
+					 * ExecCrossPartitionUpdate() must have detected that the
+					 * tuple was concurrently updated, so we restart the
+					 * search for an appropriate WHEN MATCHED clause to
+					 * process the updated tuple.
 					 *
 					 * In this case, ExecDelete() would already have performed
 					 * EvalPlanQual() on the latest version of the tuple,
 					 * which in turn would already have been loaded into
 					 * ri_oldTupleSlot, so no need to do either of those
 					 * things.
-					 *
-					 * XXX why do we not check the WHEN NOT MATCHED list in
-					 * this case?
 					 */
-					if (!TupIsNull(context->cpUpdateRetrySlot))
+					if (commandType == CMD_UPDATE &&
+						!TupIsNull(context->cpUpdateRetrySlot))
 						goto lmerge_matched;
 
 					/*
