Re: allow online change primary_conninfo

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: Sergei Kornilov <sk(at)zsrv(dot)org>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, "andres(at)anarazel(dot)de" <andres(at)anarazel(dot)de>, "david(at)pgmasters(dot)net" <david(at)pgmasters(dot)net>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>
Subject: Re: allow online change primary_conninfo
Date: 2020-03-13 14:12:04
Message-ID: 20200313141204.GA3672@alvherre.pgsql
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On 2020-Jan-22, Michael Paquier wrote:

> On Tue, Jan 21, 2020 at 06:03:18PM +0300, Sergei Kornilov wrote:
> > PS: also, I surprised why it's ok for wal_receiver_create_temp_slot
> > to be PGC_SIGHUP and ignore change of this setting until walreceiver
> > will reconnect by unrelated reason. I means walreceiver does nothing
> > special on SIGHUP. In common case change of
> > wal_receiver_create_temp_slot setting will have effect only during
> > restart of walreceiver process. And therefore we will switch to
> > archive recovery. But such design was strongly rejected for my patch
> > year ago.
> [ Looks at 3297308... ]
> Yeah, you are right. I was not paying much attention but something
> does not stick here. My understanding is that we should have the WAL
> receiver receive the value it needs to use from the startup process
> (aka via RequestXLogStreaming from xlog.c), and that we ought to make
> this new parameter PGC_POSTMASTER instead of PGC_SIGHUP. HEAD is
> inconsistent here.

I'm CCing Peter as committer of 329730827848.

What are the downsides of changing wal_receiver_create_temp_slot to
PGC_POSTMASTER? It seems pretty nasty to requires a full server
restart. Maybe we can signal all walreceivers at that point so that
they restart with the correct setting? That's much less problematic, I
would think.

Álvaro Herrera
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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