From: Tom Lane <tgl@sss.pgh.pa.us>
To: Oskari Saarenmaa <os@ohmu.fi>
cc: Robert Haas <robertmhaas@gmail.com>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Use pread and pwrite instead of lseek + write and read
In-reply-to: <6e2a5f2c-8f16-6711-717a-9c7cff45546f@ohmu.fi>
References: <a86bd200-ebbe-d829-e3ca-0c4474b2fcb7@ohmu.fi>
 <7109.1471441241@sss.pgh.pa.us>
 <CA+TgmobEq_C2t=bqBCQnwwgfXDMbbVdfndpkfyY4vCtZFveQ2A@mail.gmail.com>
 <6352.1471461075@sss.pgh.pa.us>
 <6e2a5f2c-8f16-6711-717a-9c7cff45546f@ohmu.fi>
Comments: In-reply-to Oskari Saarenmaa <os@ohmu.fi>
	message dated "Thu, 15 Sep 2016 09:55:47 +0300"
Date: Thu, 15 Sep 2016 14:11:11 -0400
Message-ID: <5806.1473963071@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Oskari Saarenmaa <os@ohmu.fi> writes:
> 17.08.2016, 22:11, Tom Lane kirjoitti:
>> I'd be more excited about this if the claimed improvement were more than
>> 1.5%, but you know as well as I do that that's barely above the noise
>> floor for most performance measurements.  I'm left wondering why bother,
>> and why take any risk of de-optimizing on some platforms.

> I think it makes sense to try to optimize for the platforms that people 
> actually use for performance critical workloads, especially if it also 
> allows us to simplify the code and remove more lines than we add.  It's 
> nice if the software still works on legacy platforms, but I don't think 
> we should be concerned about a hypothetical performance impact on 
> platforms no one uses in production anymore.

Well, my point remains that I see little value in messing with
long-established code if you can't demonstrate a benefit that's clearly
above the noise level.  We don't really know whether this change might
have adverse impacts somewhere --- either performance-wise or bug-wise ---
and for that amount of benefit I don't want to take the trouble to find
out.

			regards, tom lane


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