Re: Re: [COMMITTERS] pgsql: Make CheckRequiredParameterValues() depend upon correct

Simon Riggs wrote:
> On Thu, 2010-04-29 at 09:48 -0400, Tom Lane wrote:
>> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
>>> recovery_connections was on by default and unanimous agreement until
>>> recently and I don't want to change that now,
>> Uh, it was on by default only because a lot of us hadn't noticed that.
>> I agree with Heikki's position here: it should not be on by default.
>
> We're talking about the case where somebody has set up a standby
> database. It's not like they happen on this accidentally.
>
> * HS on by default, in the standby, via recovery_connections.
> * HS off by default, in the master, via wal_level.
>
> Overall, that *is* off by default. (Note: I said nothing about that).
>
> We don't need it off *twice*, nor do we even need two switches.

wal_level is not supposed to control if Hot Standby is on or off. It
controls what information is written to WAL. If you have
wal_level='archive' and recovery_connections='on' in the standby, that's
a configuration error, just like setting wal_level='minimal' and
archive_mode='on'. You wanted to enable Hot Standby, but the information
required isn't in the WAL.

It's error-prone to control what happens in the standby from the master.
That's the "action at a distance" effect I mentioned earlier. The master
should be configured in the master, and each standby should configured
in the standby.

The right mental model is that wal_mode controls what is written to the
WAL. In fact, I might recommend always setting it to 'hot_standby'
instead of 'archive', even if you have no standbys and you're only doing
WAL archival - it's a lot easier to do PITR with hot standby. To control
whether hot standby is enabled in the standby, use recovery_connections.
And I'd prefer it to be off by default because off is the safer option.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com