Re: pg_ctl promote wait

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Peter Eisentraut <peter_e(at)gmx(dot)net>
Cc: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_ctl promote wait
Date: 2016-02-19 20:09:58
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Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> On 2/19/16 10:06 AM, Fujii Masao wrote:
>> One concern is that there can be a "time" after the pg_control's state
>> is changed to DB_IN_PRODUCTION and before the server is able to
>> start accepting normal (not read-only) connections. So if users try to
>> start write transaction just after pg_ctl promote -w ends, they might
>> get an error because the server is still in recovery, i.e., the startup
>> process is running.

> I think that window would be acceptable.

> If not, then the way to deal with it would seem to be to create an
> entirely new mechanism to communicate with pg_ctl (e.g., a file) and
> call that at the very end of StartupXLOG(). I'm not sure that that is
> worth it.

I see no need for an additional mechanism. Just watch pg_control until
you see DB_IN_PRODUCTION state there, then switch over to the same
connection probing that "pg_ctl start -w" uses.

regards, tom lane

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