Re: recovery_connections cannot start (was Re: master in standby mode croaks)

On Fri, Apr 23, 2010 at 2:36 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
>> Tom Lane wrote:
>>> We realized some time ago that it was a good idea to separate
>>> archive_mode (what to put in WAL) from archive_command (whether we are
>>> actually archiving right now).  If we fail to apply that same principle
>>> to Hot Standby, I think we'll come to regret it.
>
>> The recovery_connections GUC does that. If you enable it, the extra
>> information required for hot standby is written to the WAL, otherwise
>> it's not.
>
> No, driving it off recovery_connections is exactly NOT that.  It's
> confusing the transport mechanism with the desired WAL contents.
> I maintain that this design is exactly isomorphic to our original PITR
> GUC design wherein what got written to WAL was determined by the current
> state of archive_command.  We eventually realized that was a bad idea.
> So is this.
>
> As a concrete example, there is nothing logically wrong with driving
> a hot standby slave from WAL records shipped via old-style pg_standby.
> Or how about wanting to turn off recovery_connections temporarily, but
> not wanting the archived WAL to be unable to support HS?

You're all confused about what the different GUCs actually do. Which
is probably not a good sign for their usability. But yeah, that's one
of the things that concerned me, too. If you turn off
max_wal_senders, it doesn't just make it so that no WAL senders can
connect: it actually changes what gets WAL-logged.

...Robert