Re: Refactor pg_rewind code and make it work against a standby

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Soumyadeep Chakraborty <soumyadeep2007(at)gmail(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Refactor pg_rewind code and make it work against a standby
Date: 2020-11-15 15:10:53
Message-ID: 037e42e3-8109-40d5-5be4-36912e5a7b69@iki.fi
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On 15/11/2020 09:07, Tom Lane wrote:
> 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?

Yep, quite right. Fixed that way, thanks for the debugging!

- Heikki

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