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Commitd8d93bc

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Avoid fetching from an already-terminated plan.
Some plan node types don't react well to being called again afterthey've already returned NULL. PortalRunSelect() has long dealtwith this by calling the executor with NoMovementScanDirectionif it sees that we've already run the portal to the end. However,commitba2c6d6 overlooked this point, so that persisting analready-fully-fetched cursor would fail if it had such a plan.Per report from Tomas Barton. Back-patch to v11, as the faultycommit was. (I've omitted a test case because the type of planthat causes a problem isn't all that stable.)Discussion:https://postgr.es/m/CAPV2KRjd=ErgVGbvO2Ty20tKTEZZr6cYsYLxgN_W3eAo9pf5sw@mail.gmail.com
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‎src/backend/commands/portalcmds.c

Lines changed: 15 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -364,6 +364,8 @@ PersistHoldablePortal(Portal portal)
364364
savePortalContext=PortalContext;
365365
PG_TRY();
366366
{
367+
ScanDirectiondirection=ForwardScanDirection;
368+
367369
ActivePortal=portal;
368370
if (portal->resowner)
369371
CurrentResourceOwner=portal->resowner;
@@ -386,10 +388,20 @@ PersistHoldablePortal(Portal portal)
386388
}
387389
else
388390
{
389-
/*We must reset the cursor state as though at start of query */
391+
/*Disallow moving backwards from here */
390392
portal->atStart= true;
391-
portal->atEnd= false;
392393
portal->portalPos=0;
394+
395+
/*
396+
* If we already reached end-of-query, set the direction to
397+
* NoMovement to avoid trying to fetch any tuples. (This check
398+
* exists because not all plan node types are robust about being
399+
* called again if they've already returned NULL once.) We'll
400+
* still set up an empty tuplestore, though, to keep this from
401+
* being a special case later.
402+
*/
403+
if (portal->atEnd)
404+
direction=NoMovementScanDirection;
393405
}
394406

395407
/*
@@ -404,7 +416,7 @@ PersistHoldablePortal(Portal portal)
404416
true);
405417

406418
/* Fetch the result set into the tuplestore */
407-
ExecutorRun(queryDesc,ForwardScanDirection,0L, false);
419+
ExecutorRun(queryDesc,direction,0L, false);
408420

409421
queryDesc->dest->rDestroy(queryDesc->dest);
410422
queryDesc->dest=NULL;

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