Horton

Re: 64-bit queryId?

Michael Paquier <michael.paquier@gmail.com>

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From: Michael Paquier <michael.paquier@gmail.com>
To: Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Peter Geoghegan <pg@bowt.ie>, Robert Haas <robertmhaas@gmail.com>, "Joshua D. Drake" <jd@commandprompt.com>, Greg Stark <stark@mit.edu>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-10-03T01:09:38Z
Lists: pgsql-hackers 
On Tue, Oct 3, 2017 at 9:07 AM, Alexander Korotkov
<a.korotkov@postgrespro.ru> wrote:
> +1,
> I see 3 options there:
> 1) Drop high-order bit, as you proposed.
> 2) Allow negative queryIds.
> 3) Implement unsigned 64-type.
>
> #1 causes minor loss of precision which looks rather insignificant in given
> context.
> #2 might be rather unexpected for users whose previously had non-negative
> queryIds.  Changing queryId from 32-bit to 64-bit itself might require some
> adoption from monitoring software. But queryIds are user-visible, and
> negative queryIds would look rather nonlogical.

Per the principal of least astonishment perhaps:
https://en.wikipedia.org/wiki/Principle_of_least_astonishment
Negative values tend to be considered as error codes as well.

> #3 would be attaching hard and long-term problem by insufficient reason.
> Thus, #1 looks like most harmless solution.

In this case going for #1 looks like the safest bet.
-- 
Michael

Commits

  1. pg_stat_statements: Add a comment about the dangers of padding bytes.

  2. pg_stat_statements: Widen query IDs from 32 bits to 64 bits.