hi, > YAMAMOTO Takashi <y...@mwd.biglobe.ne.jp> wrote: > >> it seems that PredicateLockTupleRowVersionLink sometimes create >> a loop of targets (it founds an existing 'newtarget' whose >> nextVersionOfRow chain points to the 'oldtarget') and it later >> causes CheckTargetForConflictsIn loop forever. > > Is this a hypothetical risk based on looking at the code, or have > you seen this actually happen? Either way, could you provide more > details? (A reproducible test case would be ideal.)
i have seen this actually happen. i've confirmed the creation of the loop with the attached patch. it's easily reproducable with my application. i can provide the full source code of my application if you want. (but it isn't easy to run unless you are familiar with the recent version of NetBSD) i haven't found a smaller reproducible test case yet. YAMAMOTO Takashi > > This being the newest part of the code, I'll grant that it is the > most likely to have an unidentified bug; but given that the pointers > are from one predicate lock target structure identified by a tuple > ID to one identified by the tuple ID of the next version of the row, > it isn't obvious to me how a cycle could develop. > > -Kevin
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c index 722d0f8..3e1a3e2 100644 --- a/src/backend/storage/lmgr/predicate.c +++ b/src/backend/storage/lmgr/predicate.c @@ -2350,7 +2350,25 @@ PredicateLockTupleRowVersionLink(const Relation relation, newtarget->nextVersionOfRow = NULL; } else + { Assert(newtarget->priorVersionOfRow == NULL); +#if 0 + Assert(newtarget->nextVersionOfRow == NULL); +#endif + if (newtarget->nextVersionOfRow != NULL) { + PREDICATELOCKTARGET *t; + + elog(WARNING, "new %p has next %p\n", + newtarget, newtarget->nextVersionOfRow); + for (t = newtarget->nextVersionOfRow; t != NULL; + t = t->nextVersionOfRow) { + if (oldtarget != t) { + elog(WARNING, "creating a loop new=%p old=%p\n", + newtarget, oldtarget); + } + } + } + } newtarget->priorVersionOfRow = oldtarget; oldtarget->nextVersionOfRow = newtarget;
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