Horton

Re: walsender performance regression due to logical decoding on standby changes

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Jeff Davis <pgsql@j-davis.com>
Cc: pgsql-hackers@postgresql.org, "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>
Date: 2023-05-09T21:00:24Z
Lists: pgsql-hackers 
Hi,

On 2023-05-09 13:38:24 -0700, Jeff Davis wrote:
> On Tue, 2023-05-09 at 12:02 -0700, Andres Freund wrote:
> > I don't think the approach of not having any sort of "registry" of
> > whether
> > anybody is waiting for the replay position to be updated is
> > feasible. Iterating over all walsenders slots is just too expensive -
> 
> Would it work to use a shared counter for the waiters (or, two
> counters, one for physical and one for logical), and just early exit if
> the count is zero?

That doesn't really fix the problem - once you have a single walsender
connected, performance is bad again.

Greetings,

Andres Freund

Commits

  1. Optimize walsender wake up logic using condition variables

  2. For cascading replication, wake physical and logical walsenders separately