From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexey Kondratov <a.kondratov@postgrespro.ru>
cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
        Robert Haas <robertmhaas@gmail.com>
Subject: Re: Misuse of TimestampDifference() in the autoprewarm feature of
 pg_prewarm
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Comments: In-reply-to Alexey Kondratov <a.kondratov@postgrespro.ru>
	message dated "Tue, 10 Nov 2020 19:58:44 +0300"
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Date: Tue, 10 Nov 2020 22:59:33 -0500
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Alexey Kondratov <a.kondratov@postgrespro.ru> writes:
> After looking on the autoprewarm code more closely I have realised that 
> this 'double dump' issues was not an issues at all. I have just 
> misplaced a debug elog(), so its second output in the log was only 
> indicating that we calculated delay_in_ms one more time.

Ah --- that explains why I couldn't see a problem.

I've pushed 0001+0002 plus some followup work to fix other places
that could usefully use TimestampDifferenceMilliseconds().  I have
not done anything with 0003 (the TAP test for pg_prewarm), and will
leave that to the judgment of somebody who's worked with pg_prewarm
before.  To me it looks like it's not really testing things very
carefully at all; on the other hand, we have exactly zero test
coverage of that module today, so maybe something is better than
nothing.

			regards, tom lane