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Re: Documentation on PITR still scarce

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Documentation on PITR still scarce
Date: 2004-11-29 14:01:00
Message-ID: 1101736860.2963.210.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, 2004-11-29 at 13:10, Bruce Momjian wrote:
> Or TODO maybe worded as:
> 
> 	*  Allow the PITR process to be debugged and data examined
> 

Yes, thats good for me...

Greg's additional request might be worded:

	* Allow a warm standby system to also allow read-only queries

Thanks.

> ---------------------------------------------------------------------------
> 
> Simon Riggs wrote:
> > On Mon, 2004-11-29 at 02:20, Bruce Momjian wrote:
> > 
> > > Is this a TODO?
> > 
> > Yes, but don't hold your breath on that feature.
> > 
> > Gavin and I were discussing briefly a design that would allow something
> > similar to this. The design would allow the user to stop/start recovery
> > and turn a debug trace on/off, in a gdb-like mode. Thats a lot easier to
> > implement than the proposal below, which I agree is desirable. We
> > haven't hardly started that discussion yet though.
> > I called this "recovery console" functionality.
> > 
> > I'm not sure I like the Suspended Animation phrase, I thought maybe
> > TARDIS or Langston Field sums it up better (kidding...)
> > 
> > > Greg Stark wrote:
> > > > 
> > > > Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
> > > > 
> > > > > I suppose it might be useful to have some kind of "suspended animation"
> > > > > behavior where you could bring up a backend and look at the database in
> > > > > a strict read-only fashion, not really executing transactions at all,
> > > > > just to see what you had.  Then you could end the recovery and go to
> > > > > normal operations, or allow the recovery to proceed further if you
> > > > > decided this wasn't where you wanted to be yet.  However that would
> > > > > require a great deal of mechanism we haven't got (yet).  In particular
> > > > > there is no such thing as strict read-only examination of the database.
> > > > 
> > > > That would be a great thing to have one day for other reasons aside from the
> > > > ability to test out a recovered database. It makes warm standby databases much
> > > > more useful.
> > > > 
> > > > A warm standby is when you keep a second machine constantly up to date by
> > > > applying the archived PITR logs as soon as they come off your server. You're
> > > > ready to switch over at the drop of a hat and don't have to go through the
> > > > whole recovery process, you just switch the database from recovery mode to
> > > > active mode and make it your primary database. But in the until then the
> > > > backup hardware languishes, completely useless.
> > > > 
> > > > Oracle has had a feature for a long time that you can actually open the
> > > > standby database in a strict read-only mode and run queries. This is great for
> > > > a data warehouse situation where you want to run long batch jobs against
> > > > recent data.
> > > > 
> > > >
-- 
Best Regards, Simon Riggs


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