Subject: Re: [PERFORM] Questionaire: Common WAL write rates on busy servers.
To: Andres Freund <andres@anarazel.de>, "Joshua D. Drake"
 <jd@commandprompt.com>
References: <20170425041743.ddabv2mwevcmtx5a@alap3.anarazel.de>
 <20170427155906.uudovtd62x56brmx@alap3.anarazel.de>
 <a842fbdf-b761-bf21-47dd-cd87d05a8d04@commandprompt.com>
 <20170427163407.dtqi6v57bj4tiu5c@alap3.anarazel.de>
 <80f280c1-910f-7eae-33a2-fd0cfc9ee8c9@commandprompt.com>
 <20170427173540.fqaucmclpowfy5n7@alap3.anarazel.de>
Cc: pgsql-general@postgresql.org, pgsql-performance@postgresql.org
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <cc3c764c-26a7-315c-5d81-7a84e380277a@2ndquadrant.com>
Date: Fri, 28 Apr 2017 01:29:14 +0200
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On 04/27/2017 07:35 PM, Andres Freund wrote:
> On 2017-04-27 10:29:48 -0700, Joshua D. Drake wrote:
>> On 04/27/2017 09:34 AM, Andres Freund wrote:
>>> On 2017-04-27 09:31:34 -0700, Joshua D. Drake wrote:
>>>> On 04/27/2017 08:59 AM, Andres Freund wrote:
>>>>
>>
>>>> I would agree it isn't yet a widespread issue.
>>>
>>> I'm not yet sure about that actually. I suspect a large
>>> percentage of people with such workloads aren't lingering lots on
>>> the lists.
>>
>> That would probably be true. I was thinking of it more as the
>> "most new users are in the cloud" and the "cloud" is going to be
>> rare that a cloud user is going to be able to hit that level of
>> writes. (at least not without spending LOTS of money)
>
> You can get pretty decent NVMe SSD drives on serveral cloud
> providers these days, without immediately bancrupting you. Sure, it's
> instance storage, but with a decent replication and archival setup,
> that's not necessarily an issue.
>
> It's not that hard to get to the point where postgres can't keep up
> with storage, at least for some workloads.
>

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.

regards

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


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