Horton

Re: Problem with synchronous replication

lingce.ldm <lingce.ldm@alibaba-inc.com>

View thread View on postgr.es
From: "lingce.ldm" <lingce.ldm@alibaba-inc.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, masao.fujii@gmail.com, pgsql-hackers@postgresql.org
Date: 2019-11-01T05:27:54Z
Lists: pgsql-hackers 
On Oct 31, 2019, at 10:11, Michael Paquier <michael@paquier.xyz> wrote:
> 
> On Wed, Oct 30, 2019 at 05:43:04PM +0900, Kyotaro Horiguchi wrote:
>> At Wed, 30 Oct 2019 17:21:17 +0900, Fujii Masao <masao.fujii@gmail.com> wrote in 
>>> This change causes every ending backends to always take the exclusive lock
>>> even when it's not in SyncRep queue. This may be problematic, for example,
>>> when terminating multiple backends at the same time? If yes,
>>> it might be better to check SHMQueueIsDetached() again after taking the lock.
>>> That is,
>> 
>> I'm not sure how much that harms but double-checked locking
>> (releasing) is simple enough for reducing possible congestion here, I
>> think.
> 
> FWIW, I could not measure any actual difference with pgbench -C, up to
> 500 sessions and an empty input file (just have one meta-command) and
> -c 20.
> 
> I have added some comments in SyncRepCleanupAtProcExit(), and adjusted
> the patch with the suggestion from Fujii-san.  Any comments?

Thanks for the patch. Looks good to me +1.

Regards,

—
Dongming Liu

Commits

  1. Add some assertions in syncrep.c

  2. Fix race condition at backend exit when deleting element in syncrep queue

  3. Fix typo in comment of syncrep.c