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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: Joshua D. Drake <jd@commandprompt.com>
Cc: pgsql-general@postgresql.org
Cc: pgsql-performance@postgresql.org
Subject: Re: Questionaire: Common WAL write rates on busy servers.
Date: Sat, 29 Apr 2017 02:41:19 +0200
Message-ID: <48afdba3-3429-de92-6fa8-36e2ebe5fd03@2ndquadrant.com> (raw)
In-Reply-To: <20170427233433.eg5vwlvbqyc2nruh@alap3.anarazel.de>
References: <20170425041743.ddabv2mwevcmtx5a@alap3.anarazel.de>
	<20170427155906.uudovtd62x56brmx@alap3.anarazel.de>
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	<20170427163407.dtqi6v57bj4tiu5c@alap3.anarazel.de>
	<80f280c1-910f-7eae-33a2-fd0cfc9ee8c9@commandprompt.com>
	<20170427173540.fqaucmclpowfy5n7@alap3.anarazel.de>
	<cc3c764c-26a7-315c-5d81-7a84e380277a@2ndquadrant.com>
	<20170427233433.eg5vwlvbqyc2nruh@alap3.anarazel.de>
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On 04/28/2017 01:34 AM, Andres Freund wrote:
> On 2017-04-28 01:29:14 +0200, Tomas Vondra wrote:
>> I can confirm this observation. I bought the Intel 750 NVMe SSD last year,
>> the device has 1GB DDR3 cache on it (power-loss protected), can do ~1GB/s of
>> sustained O_DIRECT sequential writes. But when running pgbench, I can't push
>> more than ~300MB/s of WAL to it, no matter what I do because of
>> WALWriteLock.
>
> Hm, interesting.  Even if you up wal_buffers to 128MB, use
> synchronous_commit = off, and play with wal_writer_delay/flush_after?
>

I think I've tried things like that, but let me do some proper testing. 
I'll report the numbers in a few days.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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