Fix possible infinite loop with Parallel Append.

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
index 64a17fb03271ac72f8bcbaedb54ccbf12225230b..264d8fea8d931de4d5c7b07e4111ead15a7c8de4 100644 (file)
--- 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;
        }