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Avoid GatherMerge crash when there are no workers. 

It's unnecessary to return an actual slot when we have no tuple.
We can just return NULL, which avoids the risk of indexing into an
array that might not contain any elements.

Rushabh Lathia, per a report from Tomas Vondra

Discussion: http://postgr.es/m/6ecd6f17-0dcf-1de7-ded8-0de7db1ddc88@2ndquadrant.com
This commit is contained in:
Robert Haas 2017-03-31 21:15:05 -04:00
parent 7d8f6986b8
commit 25dc142a49
1 changed files with 4 additions and 7 deletions
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11
src/backend/executor/nodeGatherMerge.c
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@ -419,10 +419,9 @@ reread:
}
/*
* Clear out the tuple table slots for each gather merge input,
* and return a cleared slot.
* Clear out the tuple table slots for each gather merge input.
*/
static TupleTableSlot *
static void
gather_merge_clear_slots(GatherMergeState *gm_state)
{
int i;
@ -437,9 +436,6 @@ gather_merge_clear_slots(GatherMergeState *gm_state)
pfree(gm_state->gm_tuple_buffers);
/* Free the binaryheap, which was created for sort */
binaryheap_free(gm_state->gm_heap);
/* return any clear slot */
return gm_state->gm_slots[0];
}
/*
@ -479,7 +475,8 @@ gather_merge_getnext(GatherMergeState *gm_state)
if (binaryheap_empty(gm_state->gm_heap))
{
/* All the queues are exhausted, and so is the heap */
return gather_merge_clear_slots(gm_state);
gather_merge_clear_slots(gm_state);
return NULL;
}
else
{