Fix possible infinite loop with Parallel Append.

robertmhaas · robertmhaas · commit 88fdc7006018 · 2018-02-08T12:31:48.000-05:00
When the previously-chosen plan was non-partial, all pa_finished flags for partial plans are now set, and pa_next_plan has not yet been set to INVALID_SUBPLAN_INDEX, the previous code could go into an infinite loop. Report by Rajkumar Raghuwanshi. Patch by Amit Khandekar and me. Review by Kyotaro Horiguchi. Discussion: http://postgr.es/m/CAJ3gD9cf43z78qY=U=H0HvOEN341qfRO-vLpnKPSviHeWgJQ5w@mail.gmail.com
diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
@@ -473,6 +473,9 @@ choose_next_subplan_for_worker(AppendState *node)
 		return false;
 	}
 
+	/* Save the plan from which we are starting the search. */
+	node->as_whichplan = pstate->pa_next_plan;
+
 	/* Loop until we find a subplan to execute. */
 	while (pstate->pa_finished[pstate->pa_next_plan])
 	{
@@ -481,14 +484,17 @@ choose_next_subplan_for_worker(AppendState *node)
 			/* Advance to next plan. */
 			pstate->pa_next_plan++;
 		}
-		else if (append->first_partial_plan < node->as_nplans)
+		else if (node->as_whichplan > append->first_partial_plan)
 		{
 			/* Loop back to first partial plan. */
 			pstate->pa_next_plan = append->first_partial_plan;
 		}
 		else
 		{
-			/* At last plan, no partial plans, arrange to bail out. */
+			/*
+			 * At last plan, and either there are no partial plans or we've
+			 * tried them all.  Arrange to bail out.
+			 */
 			pstate->pa_next_plan = node->as_whichplan;
 		}
 

Original file line number	Diff line number	Diff line change
`@@ -473,6 +473,9 @@ choose_next_subplan_for_worker(AppendState *node)`
`473`	`473`	`return false;`
`474`	`474`	`}`
`475`	`475`
	`476`	`+ /* Save the plan from which we are starting the search. */`
	`477`	`+ node->as_whichplan = pstate->pa_next_plan;`
	`478`	`+`
`476`	`479`	`/* Loop until we find a subplan to execute. */`
`477`	`480`	`while (pstate->pa_finished[pstate->pa_next_plan])`
`478`	`481`	`{`
`@@ -481,14 +484,17 @@ choose_next_subplan_for_worker(AppendState *node)`
`481`	`484`	`/* Advance to next plan. */`
`482`	`485`	`pstate->pa_next_plan++;`
`483`	`486`	`}`
`484`		`- else if (append->first_partial_plan < node->as_nplans)`
	`487`	`+ else if (node->as_whichplan > append->first_partial_plan)`
`485`	`488`	`{`
`486`	`489`	`/* Loop back to first partial plan. */`
`487`	`490`	`pstate->pa_next_plan = append->first_partial_plan;`
`488`	`491`	`}`
`489`	`492`	`else`
`490`	`493`	`{`
`491`		`- /* At last plan, no partial plans, arrange to bail out. */`
	`494`	`+ /*`
	`495`	`+ * At last plan, and either there are no partial plans or we've`
	`496`	`+ * tried them all. Arrange to bail out.`
	`497`	`+ */`
`492`	`498`	`pstate->pa_next_plan = node->as_whichplan;`
`493`	`499`	`}`
`494`	`500`