Feedback-ID: id4a34324:Fastmail
Date: Sun, 2 Apr 2023 15:29:04 -0700
From: Andres Freund <andres@anarazel.de>
To: Jeff Davis <pgsql@j-davis.com>
Cc: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>,
	Robert Haas <robertmhaas@gmail.com>,
	Thomas Munro <thomas.munro@gmail.com>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	Ibrar Ahmed <ibrar.ahmad@gmail.com>,
	Amit Khandekar <amitdkhan.pg@gmail.com>, fabriziomello@gmail.com,
	tushar <tushar.ahuja@enterprisedb.com>,
	Rahila Syed <rahila.syed@2ndquadrant.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Minimal logical decoding on standbys
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Hi,

On 2023-04-02 15:15:44 -0700, Jeff Davis wrote:
> On Sun, 2023-04-02 at 14:35 -0700, Andres Freund wrote:
> > Why not offer a function to add a CV to a WES? It seems somehow odd
> > to require
> > going through condition_variable.c to create a WES.
> 
> I agree that it's a bit odd, but remember that after waiting on a CV's
> latch, it needs to re-insert itself into the CV's wait list.
> 
> A WaitEventSetWait() can't do that, unless we move the details of re-
> adding to the wait list into latch.c. I considered that, but latch.c
> already implements the APIs for WaitEventSet and Latch, so it felt
> complex to also make it responsible for ConditionVariable.

I agree that the *wait* has to go through condition_variable.c, but it doesn't
seem right that creation of the WES needs to go through condition_variable.c.

The only thing that ConditionVariableEventSleep() seems to require is that the
WES is waiting for MyLatch. You don't even need a separate WES for that, the
already existing WES should suffice.

Greetings,

Andres Freund