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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Soumyadeep Chakraborty <soumyadeep2007@gmail.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Refactor pg_rewind code and make it work against a standby
Date: Sun, 15 Nov 2020 02:07:02 -0500
Message-ID: <606796.1605424022@sss.pgh.pa.us> (raw)
In-Reply-To: <605973.1605422900@sss.pgh.pa.us>
References: <0c5b3783-af52-3ee5-f8fa-6e794061f70d@iki.fi>
	<20200820.173224.2258034742176021277.horikyota.ntt@gmail.com>
	<f155aab5-1323-8d0c-9e3b-32703124bf00@iki.fi>
	<20200918.164150.1688011206252014871.horikyota.ntt@gmail.com>
	<CAE-ML+-uLy_DiS4VSkbsjMEY9ZBob5LqBXPc31_dQ-EsSesgEw@mail.gmail.com>
	<4744063e-1a60-1b24-e1b7-7ace5e65f0d2@iki.fi>
	<CAE-ML+9NG=HnLq8P_sHM=9UFUPnWbQDSRnmZrMPXONERVJS+zQ@mail.gmail.com>
	<da768d3a-dddc-fd3f-4b64-e951a1926bfa@iki.fi>
	<95c2ad04-eb6b-7c2e-b751-c65acccd81df@iki.fi>
	<605973.1605422900@sss.pgh.pa.us>

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





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  Cc: tgl@sss.pgh.pa.us, hlinnaka@iki.fi, soumyadeep2007@gmail.com, horikyota.ntt@gmail.com
  Subject: Re: Refactor pg_rewind code and make it work against a standby
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