| From: | Michael Paquier <michael(at)paquier(dot)xyz> |
|---|---|
| To: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> |
| Cc: | masao(dot)fujii(at)gmail(dot)com, lingce(dot)ldm(at)alibaba-inc(dot)com, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Problem with synchronous replication |
| Date: | 2019-10-31 02:11:03 |
| Message-ID: | 20191031021103.GC2530@paquier.xyz |
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| Lists: | pgsql-hackers |
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(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.
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?
--
Michael
| Attachment | Content-Type | Size |
|---|---|---|
| syncrep-lwlocks-v2.patch | text/x-diff | 2.6 KB |
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