Feedback-ID: i0fe9450f:Fastmail
Date: Fri, 28 Feb 2025 14:41:34 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: [BUG]: the walsender does not update its IO statistics until it
 exits
Message-ID: <Z8FMjlyNpNicucGa@paquier.xyz>
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On Wed, Feb 26, 2025 at 09:48:50AM +0000, Bertrand Drouvot wrote:
> Yeah I think that makes sense, done that way in the attached.
>=20
> Speaking about physical walsender, I moved the test to 001_stream_rep.pl =
instead
> (would also fail without the fix).

Hmm.  I was doing some more checks with this patch, and on closer look
I am wondering if the location you have chosen for the stats reports
is too aggressive: this requires a LWLock for the WAL sender backend
type taken in exclusive mode, with each step of WalSndLoop() taken
roughly each time a record or a batch of records is sent.  A single
installcheck with a primary/standby setup can lead to up to 50k stats
report calls.

With smaller records, the loop can become hotter, can't it?  Also,
there can be a high number of WAL senders on a single node, and I've
heard of some customers with complex logical decoding deployments with
dozens of logical WAL senders.  Isn't there a risk of having this code
path become a point of contention?  It seems to me that we should
benchmark this change more carefully, perhaps even reduce the
frequency of the report calls.
--
Michael

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