Re: ALTER TABLE lock strength reduction patch is unsafe

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: Noah Misch <noah(at)leadboat(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: ALTER TABLE lock strength reduction patch is unsafe
Date: 2012-01-02 20:20:08
Message-ID: 1310.1325535608@sss.pgh.pa.us
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Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> On Mon, Jan 2, 2012 at 7:14 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> But you still didn't. I wanted to know what those numbers were and how
>> they show that there's not a performance regression. Presumably you
>> meant that some were "before" and some "after", but they were not so
>> labeled.

> All timings were "after" applying the patch. Since all of the tests
> had very acceptable absolute values I didn't test without-patch.

What is a "very acceptable absolute value", and how do you know it's
acceptable if you don't know what the previous performance was? This
reasoning makes no sense to me at all.

regards, tom lane

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