Date: Wed, 24 Jan 2018 10:28:41 -0800
From: Andres Freund <andres@anarazel.de>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
	Thomas Munro <thomas.munro@enterprisedb.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: pgsql: Add parallel-aware hash joins.
Message-ID: <20180124182841.ep7yr6tgqazsoilu@alap3.anarazel.de>
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Hi,

On 2018-01-24 13:11:22 -0500, Robert Haas wrote:
> So for me, the additional hash index tests don't cost anything
> measurable and the additional hash join tests cost about a second.  I
> think this probably accounts for why committers other than you keep
> "adding so much time to the regression tests".  On modern hardware,
> the costs just don't matter.

I very much agree with the general sentiment, but a second of a 25s test
certainly isn't nothing.  As I've just written a few messages upthread,
I think we can hide the overall timing costs to a much larger degree
than we're doing, but I don't think we need not pay attention at all.


> Now, how much should we care about the performance of software with a
> planned release date of 2018 on hardware discontinued in 2001,
> hardware that is apparently about 20 times slower than a modern
> laptop?  Some, perhaps, but maybe not a whole lot.  Removing tests
> that have found actual bugs because they cost runtime on ancient
> systems that nobody uses for serious work doesn't make sense to me.

I again agree with the sentiment. One caveat is that old machines also
somewhat approximate testing with more instrumentation / debugging
enabled (say valgrind, CLOBBER_CACHE_ALWAYS, etc). So removing excessive
test overhead has still quite some benefits. But I definitely do not
want to lower coverage to achieve it.

Greetings,

Andres Freund