Subject: Re: pg_get_wal_replay_pause_state() should not return 'paused' while
 a promotion is ongoing.
To: Michael Paquier <michael@paquier.xyz>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, pgsql-hackers@postgresql.org
References: <f706876c-4894-0ba5-6f4d-79803eeea21b@oss.nttdata.com>
 <20210518.095805.1634592437754592061.horikyota.ntt@gmail.com>
 <ce4ce624-be5c-c9fa-919c-e0a646c5d03c@oss.nttdata.com>
 <YKNirzqM1HYyk5h4@paquier.xyz>
From: Fujii Masao <masao.fujii@oss.nttdata.com>
Message-ID: <34ecf08e-3f3b-0fd6-30e1-678208b618f2@oss.nttdata.com>
Date: Wed, 19 May 2021 13:46:45 +0900
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On 2021/05/18 15:46, Michael Paquier wrote:
> On Tue, May 18, 2021 at 12:48:38PM +0900, Fujii Masao wrote:
>> Currently a promotion causes all available WAL to be replayed before
>> a standby becomes a primary whether it was in paused state or not.
>> OTOH, something like immediate promotion (i.e., standby becomes
>> a primary without replaying outstanding WAL) might be useful for
>> some cases. I don't object to that.
> 
> Sounds like a "promotion immediate" mode.  It does not sound difficult
> nor expensive to add a small test for that in one of the existing
> recovery tests triggerring a promotion.  Could you add one based on
> pg_get_wal_replay_pause_state()?

You're thinking to add the test like the following?
#1. Pause the recovery
#2. Confirm that pg_get_wal_replay_pause_state() returns 'paused'
#3. Trigger standby promotion
#4. Confirm that pg_get_wal_replay_pause_state() returns 'not paused'

It seems not easy to do the test #4 stably because
pg_get_wal_replay_pause_state() needs to be executed
before the promotion finishes.

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION