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Commit29f9fb8

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Allow special SKIP LOCKED condition in Assert()
Under concurrency, it is possible for two sessions to be merrily lockingand releasing a tuple and marking it again as HEAP_XMAX_INVALID all thewhile a third session attempts to lock it, miserably fails at it, andthen contemplates life, the universe and everything only to eventuallyfail an assertion that said bit is not set. Before SKIP LOCKED that wasindeed a reasonable expectation, but alas! commitdf630b0 falsifiedit.This bug is as old as time itself, and even older, if you think timebegins with the oldest supported branch. Therefore, backpatch to allsupported branches.Author: Simon Riggs <simon.riggs@enterprisedb.com>Discussion:https://postgr.es/m/CANbhV-FeEwMnN8yuMyss7if1ZKjOKfjcgqB26n8pqu1e=q0ebg@mail.gmail.com
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‎src/backend/access/heap/heapam.c

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4497,7 +4497,15 @@ heap_lock_tuple(Relation relation, HeapTuple tuple,
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{
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Assert(result==TM_SelfModified||result==TM_Updated||
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result==TM_Deleted||result==TM_WouldBlock);
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Assert(!(tuple->t_data->t_infomask&HEAP_XMAX_INVALID));
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/*
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* When locking a tuple under LockWaitSkip semantics and we fail with
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* TM_WouldBlock above, it's possible for concurrent transactions to
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* release the lock and set HEAP_XMAX_INVALID in the meantime. So
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* this assert is slightly different from the equivalent one in
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* heap_delete and heap_update.
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*/
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Assert(TM_WouldBlock|| !(tuple->t_data->t_infomask&HEAP_XMAX_INVALID));
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Assert(result!=TM_Updated||
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!ItemPointerEquals(&tuple->t_self,&tuple->t_data->t_ctid));
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tmfd->ctid=tuple->t_data->t_ctid;

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