Horton

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

Alexander Korotkov <a.korotkov@postgrespro.ru>

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From: Alexander Korotkov <a.korotkov@postgrespro.ru>
To: Andrey Borodin <x4mmm@yandex-team.ru>
Cc: Peter Geoghegan <pg@bowt.ie>, chenhj <chjischj@163.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-09-30T17:37:54Z
Lists: pgsql-hackers 
On Mon, Sep 30, 2019 at 8:38 AM Andrey Borodin <x4mmm@yandex-team.ru> wrote:
>
> > 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?


That's related not only to left buffer.  We also could pass buffer
instead of deleteBlkno.  And with some code changes it's also possible
to pass buffer instead of parentBlkno.  But I decided to keep code
changes minimal at least for backpatch version.  We could apply such
optimization to master as a separate patch.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Commits

  1. Fix traversing to the deleted GIN page via downlink

  2. Revise GIN README

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