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From: Nathan Bossart <[email protected]>
To: Bharath Rupireddy <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: WAL Insertion Lock Improvements (was: Re: Avoid LWLockWaitForVar() for currently held WAL insertion lock in WaitXLogInsertionsToFinish())
Date: Fri, 2 Dec 2022 16:31:58 -0800
Message-ID: <20221203003158.GA2518778@nathanxps13> (raw)
In-Reply-To: <CALj2ACXYpYDboe4i+yXDYoNQj9-G0584hP5x_b=W6hj693qcaA@mail.gmail.com>
References: <CALj2ACVF+6jLvqKe6xhDzCCkr=rfd6upaGc3477Pji1Ke9G7Bg@mail.gmail.com>
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	<CALj2ACWkWbheFhkPwMw83CUpzHFGXSV_HXTBxG9+-PZ3ufHE=Q@mail.gmail.com>
	<[email protected]>
	<CALj2ACXYpYDboe4i+yXDYoNQj9-G0584hP5x_b=W6hj693qcaA@mail.gmail.com>

On Fri, Dec 02, 2022 at 04:32:38PM +0530, Bharath Rupireddy wrote:
> On Fri, Dec 2, 2022 at 6:10 AM Andres Freund <[email protected]> wrote:
>> I'm not sure this is quite right - don't we need a memory barrier. But I don't
>> see a reason to not just leave this code as-is. I think this should be
>> optimized entirely in lwlock.c
> 
> Actually, we don't need that at all as LWLockWaitForVar() will return
> immediately if the lock is free. So, I removed it.

I briefly looked at the latest patch set, and I'm curious how this change
avoids introducing memory ordering bugs.  Perhaps I am missing something
obvious.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

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