Subject: Re: pg_get_wal_replay_pause_state() should not return 'paused' while
 a promotion is ongoing.
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: pgsql-hackers@postgresql.org
References: <f706876c-4894-0ba5-6f4d-79803eeea21b@oss.nttdata.com>
 <20210518.095805.1634592437754592061.horikyota.ntt@gmail.com>
From: Fujii Masao <masao.fujii@oss.nttdata.com>
Message-ID: <ce4ce624-be5c-c9fa-919c-e0a646c5d03c@oss.nttdata.com>
Date: Tue, 18 May 2021 12:48:38 +0900
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:78.0)
 Gecko/20100101 Thunderbird/78.10.1
MIME-Version: 1.0
In-Reply-To: <20210518.095805.1634592437754592061.horikyota.ntt@gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Archived-At: 
 <https://www.postgresql.org/message-id/ce4ce624-be5c-c9fa-919c-e0a646c5d03c%40oss.nttdata.com>
Precedence: bulk


On 2021/05/18 9:58, Kyotaro Horiguchi wrote:
> At Mon, 17 May 2021 23:29:18 +0900, Fujii Masao <masao.fujii@oss.nttdata.com> wrote in
>> If a promotion is triggered while recovery is paused, the paused state
>> ends
>> and promotion continues. But currently pg_get_wal_replay_pause_state()
>> returns 'paused' in that case. Isn't this a bug?
>>
>> Attached patch fixes this issue by resetting the recovery pause state
>> to
>> 'not paused' when standby promotion is triggered.
>>
>> Thought?
> 
> Nice catch!
> 
> Once the state enteres "paused" state no more WAL record is expected
> to be replayed until exiting the state. I'm not sure but maybe we are
> also expecting that the server promotes whthout a record replayed when
> triggered while pausing.

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.

Regards,

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