From: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> |
---|---|
To: | masao(dot)fujii(at)gmail(dot)com |
Cc: | lingce(dot)ldm(at)alibaba-inc(dot)com, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Problem with synchronous replication |
Date: | 2019-10-30 08:43:04 |
Message-ID: | 20191030.174304.523404903817205414.horikyota.ntt@gmail.com |
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Thread: | |
Lists: | pgsql-hackers |
Hello.
At Wed, 30 Oct 2019 17:21:17 +0900, Fujii Masao <masao(dot)fujii(at)gmail(dot)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. In short, + 1 for that.
> if (!SHMQueueIsDetached(&(MyProc->syncRepLinks)))
> {
> LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
> if (!SHMQueueIsDetached(&(MyProc->syncRepLinks)))
> SHMQueueDelete(&(MyProc->syncRepLinks));
> LWLockRelease(SyncRepLock);
> }
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
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