Horton

Re: Connections hang indefinitely while taking a gin index's LWLock buffer_content lock(PG10.7)

x4mmm@yandex-team.ru

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From: Andrey Borodin <x4mmm@yandex-team.ru>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>, chenhj <chjischj@163.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-09-30T05:38:10Z
Lists: pgsql-hackers 

> 29 сент. 2019 г., в 21:27, Alexander Korotkov <a.korotkov@postgrespro.ru> написал(а):
> 
> Patch with fix is attached.  Idea is simple: ginScanToDelete() now
> keeps exclusive lock on left page eliminating the need to relock it.
> So, we preserve left-to-right locking order and can't deadlock with
> ginStepRight().

In this function ginDeletePage(gvs, blkno, BufferGetBlockNumber(me->leftBuffer),...)
we are going to reread buffer
lBuffer = ReadBufferExtended(gvs->index, MAIN_FORKNUM, leftBlkno,
                                 RBM_NORMAL, gvs->strategy);
Is it OK?


> 30 сент. 2019 г., в 0:52, Peter Geoghegan <pg@bowt.ie> написал(а):
> 
> Why is it okay
> that there is no nbtree-style distinction between page deletion and
> page recycling?
As far as I understand deleted page is stamped with
GinPageSetDeleteXid(page, ReadNewTransactionId());
It will not be recycled until that Xid is far behind.
BTW we found a small bug (wraparound) in similar GiST and B-tree implementations.
Probably, it's there in GIN too.

--
Andrey Borodin
Open source RDBMS development team leader
Yandex.Cloud

Commits

  1. Fix traversing to the deleted GIN page via downlink

  2. Revise GIN README

  3. Fix deadlock between ginDeletePage() and ginStepRight()