From: Tom Lane <tgl@sss.pgh.pa.us>
To: Heikki Linnakangas <hlinnaka@iki.fi>
cc: Soumyadeep Chakraborty <soumyadeep2007@gmail.com>,
        Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Refactor pg_rewind code and make it work against a standby
In-reply-to: <605973.1605422900@sss.pgh.pa.us>
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Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Sun, 15 Nov 2020 01:48:20 -0500"
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Date: Sun, 15 Nov 2020 02:07:02 -0500
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I wrote:
> Not sure if you noticed, but piculet has twice failed the
> 007_standby_source.pl test that was added by 9c4f5192f:
> ...
> Now, I'm not sure what to make of that, but I can't help noticing that
> piculet uses --disable-atomics while francolin uses --disable-spinlocks.
> That leads the mind towards some kind of low-level synchronization
> bug ...

Or, maybe it's less mysterious than that.  The failure looks like we
have not waited long enough for the just-inserted row to get replicated
to node C.  That wait is implemented as

	$lsn = $node_a->lsn('insert');
	$node_b->wait_for_catchup('node_c', 'write', $lsn);

which looks fishy ... shouldn't wait_for_catchup be told to
wait for replay of that LSN, not just write-the-WAL?

			regards, tom lane