Horton

Re: Connections hang indefinitely while taking a gin index's LWLock buffer_content lock

Peter Geoghegan <pg@bowt.ie>

View thread View on postgr.es
From: Peter Geoghegan <pg@bowt.ie>
To: aekorotkov@gmail.com
Cc: Andres Freund <andres@anarazel.de>, chjischj@163.com, Teodor Sigaev <teodor@sigaev.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2018-12-06T21:50:11Z
Lists: pgsql-hackers 
On Thu, Dec 6, 2018 at 12:51 PM Alexander Korotkov <aekorotkov@gmail.com> wrote:
> So, algorithm introduced by 218f51584d5 is broken.  It tries to
> guarantee that there are no inserters in the subtree by placing
> cleanup lock to subtree root, assuming that inserter holds pins on the
> path from root to leaf.  But due to concurrent splits of internal
> pages the pins held can be not relevant to actual path.  I don't see
> the way to fix this easily.  So, I think we should revert it from back
> branches and try to reimplement that in master.
>
> However, I'd like to note that 218f51584d5 introduces two changes:
> 1) Cleanup locking only if there pages to delete
> 2) Cleanup locking only subtree root
> The 2nd one is broken.  But the 1st one seems still good for me and
> useful, because in vast majority of cases vacuum doesn't delete any
> index pages.  So, I propose to revert 218f51584d5, but leave there
> logic, which locks root for cleanup only once there are pages to
> delete.  Any thoughts?

Can you post a patch that just removes the 2nd part, leaving the
still-correct first part?

Your proposal sounds reasonable, but I'd like to see what you have in
mind in detail before commenting.

Thanks
-- 
Peter Geoghegan

Commits

  1. Fix WAL format incompatibility introduced by backpatching of 52ac6cd2d0

  2. Fix wrong backpatching of ginRedoDeletePage() deadlock fix

  3. Fix deadlock in GIN vacuum introduced by 218f51584d5

  4. Prevent GIN deleted pages from being reclaimed too early

  5. Prevent deadlock in ginRedoDeletePage()

  6. Reduce page locking in GIN vacuum

  7. Fix race condition in GIN posting tree page deletion.