Date: Wed, 16 Feb 2022 08:44:42 -0800
From: Nathan Bossart <nathandbossart@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@gmail.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: USE_BARRIER_SMGRRELEASE on Linux?
Message-ID: <20220216164442.GA2935315@nathanxps13>
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On Tue, Feb 15, 2022 at 10:57:32PM -0800, Nathan Bossart wrote:
> On Tue, Feb 15, 2022 at 10:14:04PM -0800, Nathan Bossart wrote:
>> It looks like register_unlink_segment() is called prior to the checkpoint,
>> but the checkpointer is not calling RememberSyncRequest() until after
>> SyncPreCheckpoint().  This means that the requests are registered with the
>> next checkpoint cycle count, so they aren't processed until the next
>> checkpoint.
> 
> Calling AbsorbSyncRequests() before advancing the checkpoint cycle counter
> seems to fix the issue.  However, this requires moving SyncPreCheckpoint()
> out of the critical section in CreateCheckPoint().  Patch attached.

An alternative fix might be to call AbsorbSyncRequests() after increasing
the ckpt_started counter in CheckpointerMain().  AFAICT there is a window
just before checkpointing where new requests are registered for the
checkpoint following the one about to begin.

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