Re: Improving connection scalability: GetSnapshotData()

From: Andres Freund <andres(at)anarazel(dot)de>
To: Ian Barwick <ian(dot)barwick(at)2ndquadrant(dot)com>, andrew(at)dunslane(dot)net
Cc: Michael Paquier <michael(at)paquier(dot)xyz>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, "Jonathan S(dot) Katz" <jkatz(at)postgresql(dot)org>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Peter Geoghegan <pg(at)bowt(dot)ie>, Bruce Momjian <bruce(at)momjian(dot)us>, David Rowley <dgrowleyml(at)gmail(dot)com>
Subject: Re: Improving connection scalability: GetSnapshotData()
Date: 2020-10-01 18:26:30
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Hi Ian, Andrew, All,

On 2020-09-30 15:43:17 -0700, Andres Freund wrote:
> Attached is an updated version of the test (better utility function,
> stricter regexes, bailing out instead of failing just the current when
> psql times out). I'm leaving it in this test for now, but it's fairly
> easy to use this way, in my opinion, so it may be worth moving to
> PostgresNode at some point.

I pushed this yesterday. Ian, thanks again for finding this and helping
with fixing & testing.

Unfortunately currently some buildfarm animals don't like the test for
reasons I don't quite understand. Looks like it's all windows + msys
animals that run the tap tests. On jacana and fairywren the new test
fails, but with a somewhat confusing problem:
Bail out! aborting wait: program timed out
# stream contents: >>data
# (0 rows)
# <<
# pattern searched for: (?m-xis:^\\(0 rows\\)$)
Bail out! aborting wait: program timed out
stream contents: >>data
(0 rows)
pattern searched for: (?^m:^\\(0 rows\\)$)

I don't know with the -xis indicates on jacana, and why it's not present
on fairywren. Nor do I know why the pattern doesn't match in the first
place, sure looks like it should?

Andrew, do you have an insight into how mingw's regex match differs
from native windows and proper unixoid systems? I guess it's somewhere
around line endings or such?

Jacana successfully deals with, which does use the
same mechanis as the new - I think the only real
difference is that I used ^ and $ in the regexes in the latter...


Andres Freund

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