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

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: [COMMITTERS] pgsql: Make CheckRequiredParameterValues() depend upon correct
Date: 2010-04-29 10:46:32
Message-ID: 4BD96388.8070203@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
Simon Riggs wrote:
> The whole point of
> wal_level discussion was to avoid needing multiple switches to turn
> something on.

No, the point of wal_level was to make the behavior easier to
understand, by uncoupling the level of WAL-logging from various other
switches, controling it directly and explicitly with a new GUC instead.
It added a new switch, but made the system as a whole easier to
understand and configure.

>> > I can't imagine a situation where "allow connections if the WAL allows
>> > it" would be a sensible setting. If there is one, we could have an
>> > 'auto' mode, but not as the default.
> 
> I can. Simple, obvious behaviour. Turn it on in the master, works on the
> standbys.

Yes, but when would you want that?

Here's the use cases I can think of:

purpose of the standby - do you want hot standby or not?
reporting - yes
offloading queries from master - yes
warm standby for high availability - no
offloading taking filesystem-level backups from master - no
offloading pg_dump from master - yes

All of those either want hot standby, or don't. What use case is there
for "enabled, if the required information is in the WAL"? If there is
one, it sure doesn't seem like the most common one. When you just want
hot standby to be on or off, it's weird to control that from the master.
Action at a distance.

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

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