Re: Improving connection scalability: GetSnapshotData()

From: Andres Freund <andres(at)anarazel(dot)de>
To: Ian Barwick <ian(dot)barwick(at)2ndquadrant(dot)com>
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: 2020-09-30 22:43:17
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On 2020-09-14 16:17:18 -0700, Andres Freund wrote:
> I've also included a quite heavily revised version of your test. Instead
> of using dblink I went for having a long-running psql that I feed over
> stdin. The main reason for not liking the previous version is that it
> seems fragile, with the sleep and everything. I expanded it to cover
> 2PC is as well.
> The test probably needs a bit of cleanup, wrapping some of the
> redundancy around the pump_until calls.
> I think the approach of having a long running psql session is really
> useful, and probably would speed up some tests. Does anybody have a good
> idea for how to best, and without undue effort, to integrate this into
> I don't really have a great idea, so I think I'd leave
> it with a local helper in the new test?

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.


Andres Freund

Attachment Content-Type Size
v3-0001-Fix-and-test-snapshot-behaviour-on-standby.patch text/x-diff 7.7 KB

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