Subject: Re: what to revert
To: Andres Freund <andres@anarazel.de>
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Cc: pgsql-hackers@postgresql.org
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <eb3d6105-7165-fe71-f753-0a95281c3c19@2ndquadrant.com>
Date: Sat, 7 May 2016 02:54:18 +0200
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Hi,

On 05/04/2016 12:42 AM, Andres Freund wrote:
> On 2016-05-03 20:57:13 +0200, Tomas Vondra wrote:
>> On 05/03/2016 07:41 PM, Andres Freund wrote:
...
>>> I'm pretty sure that I said that somewhere else at least once: But to
>>> be absolutely clear, I'm *not* really concerned with the performance
>>> with the feature turned off. I'm concerned about the performance with
>>> it turned on.
>>
>> If you tell me how to best test it, I do have a 4-socket server sitting idly
>> in the corner (well, a corner reachable by SSH). I can get us some numbers,
>> but I haven't been following the snapshot_too_old so I'll need some guidance
>> on what to test.
>
> I think it'd be cool if you could test the effect of the feature in
> read-only (and additionally read-mostly?) workload with various client
> counts and snapshot_too_old values. For the latter maybe -1, 0, 10, 60
> or such?  I've done so (accidentally comparing 0 and 1 instead of -1 and
> 1) on a two socket machine in:
> www.postgresql.org/message-id/20160413171955.i53me46fqqhdlztq@alap3.anarazel.de
>
> It'd be very interesting to see how big the penalty is on a bigger box.

OK. I do have results from mater with different values for the GUC (-1, 
0, 10, 60), but I'm struggling with the reverts. Can you provide a patch 
against current master (commit 4bbc1a7e) that does the revert?

regards

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


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