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Re: [COMMITTERS] pgsql: Remove too-smart-for-its-own-good optimization of not overwriting

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [COMMITTERS] pgsql: Remove too-smart-for-its-own-good optimization of not overwriting
Date: 2010-01-05 03:54:20
Message-ID: 603c8f071001041954s77147c92y94e866b9641b14f7@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
On Mon, Jan 4, 2010 at 10:51 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Mon, Jan 4, 2010 at 9:34 PM, Tom Lane <tgl(at)postgresql(dot)org> wrote:
>>> Log Message:
>>> -----------
>>> Remove too-smart-for-its-own-good optimization of not overwriting the output
>>> files when they haven't changed.  This confuses make because the build fails
>>> to update the file timestamps, and so it keeps on doing the action over again.
>
>> This doesn't seem like a good idea.
>
> The original code was a bad idea, written by someone who was a
> self-acknowledged non expert on make.  The way that you avoid
> unnecessary recompilations is by not changing the input files,
> not by breaking the file timestamp relationships that make depends
> on to work sanely.

I think you're dismissing the idea too cavalierly.  If A generates B,
A is inevitably changed frequently, but the changes to A affect B only
rarely, this is a good trick.

...Robert

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