From: Sergei Kornilov <sk@zsrv.org>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>,
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	=?utf-8?B?w4FsdmFybyBIZXJyZXJh?= <alvherre@2ndquadrant.com>
References: 
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	 <20200310.175755.1250389993502025042.horikyota.ntt@gmail.com>
	 <aa078efe-2d25-fdab-5bdb-158edab5d849@2ndquadrant.com>
	 <20200311.110637.1319131984113864409.horikyota.ntt@gmail.com>
	 <2134a29f-e934-4585-e81f-ab416e1923be@2ndquadrant.com>
	 <CA+fd4k4G3pAY+KPDzNRCGu=FZQT81KhXT-8EcjYGpc6cpmiT9w@mail.gmail.com>
	 <2808491585335240@iva3-67f911cb3a01.qloud-c.yandex.net>
	 <f71030f1-cd0a-5e7c-5d09-cbebc6603bf5@2ndquadrant.com>
	 <ddd72267-d4cb-4b4e-07af-4685316a2c92@2ndquadrant.com>
	 <5e93f9f5-9572-38d0-b740-f8a20dfcc165@2ndquadrant.com>
	 <2985371605808012@mail.yandex.ru>
 <c3375379-d699-c514-9664-defbb92ec344@2ndquadrant.com>
Subject: Re: Improve handling of parameter differences in physical replication
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Date: Fri, 20 Nov 2020 18:47:59 +0300
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Hello

> I think I like "unpaused" better here, because "resumed" would seem to
> imply that recovery can actually continue.

Good, I agree.

> One thing that has not been added to my patch is the equivalent of
> 496ee647ecd2917369ffcf1eaa0b2cdca07c8730, which allows promotion while
> recovery is paused. I'm not sure that would be necessary, and it
> doesn't look easy to add either.

Hmm... Good question. How about putting CheckForStandbyTrigger() in a wait loop, but reporting FATAL with an appropriate message, such as "promotion is not possible because of insufficient parameter settings"?
Also it suits me if we only document that we ignore promote here. I don't think this is an important case. And yes, it's not easy to allow promotion, since we have already updated control file.

Probably we need pause only after we reached consistency?

2020-11-20 18:10:23.617 MSK 19722 @ from  [vxid: txid:0] [] LOG:  entering standby mode
2020-11-20 18:10:23.632 MSK 19722 @ from  [vxid: txid:0] [] WARNING:  hot standby is not possible because of insufficient parameter settings
2020-11-20 18:10:23.632 MSK 19722 @ from  [vxid: txid:0] [] DETAIL:  max_connections = 100 is a lower setting than on the primary server, where its value was 150.
2020-11-20 18:10:23.632 MSK 19722 @ from  [vxid: txid:0] [] LOG:  recovery has paused
2020-11-20 18:10:23.632 MSK 19722 @ from  [vxid: txid:0] [] DETAIL:  If recovery is unpaused, the server will shut down.
2020-11-20 18:10:23.632 MSK 19722 @ from  [vxid: txid:0] [] HINT:  You can then restart the server after making the necessary configuration changes.
2020-11-20 18:13:09.767 MSK 19755 melkij@postgres from [local] [vxid: txid:0] [] FATAL:  the database system is starting up

regards, Sergei