Re: Time-Delayed Standbys

On 2013-12-03 13:46:28 -0500, Robert Haas wrote:
> On Tue, Dec 3, 2013 at 12:36 PM, Fabrízio de Royes Mello
> <fabriziomello@gmail.com> wrote:
> > On Tue, Dec 3, 2013 at 2:33 PM, Christian Kruse <christian@2ndquadrant.com>
> > wrote:
> >>
> >> Hi Fabrizio,
> >>
> >> looks good to me. I did some testing on 9.2.4, 9.2.5 and HEAD. It
> >> applies and compiles w/o errors or warnings. I set up a master and two
> >> hot standbys replicating from the master, one with 5 minutes delay and
> >> one without delay. After that I created a new database and generated
> >> some test data:
> >>
> >> CREATE TABLE test (val INTEGER);
> >> INSERT INTO test (val) (SELECT * FROM generate_series(0, 1000000));
> >>
> >> The non-delayed standby nearly instantly had the data replicated, the
> >> delayed standby was replicated after exactly 5 minutes. I did not
> >> notice any problems, errors or warnings.
> >>
> >
> > Thanks for your review Christian...
>
> So, I proposed this patch previously and I still think it's a good
> idea, but it got voted down on the grounds that it didn't deal with
> clock drift.  I view that as insufficient reason to reject the
> feature, but others disagreed.

I really fail to see why clock drift should be this patch's
responsibility. It's not like the world would go under^W data corruption
would ensue if the clocks drift. Your standby would get delayed
imprecisely. Big deal. From what I know of potential users of this
feature, they would set it to at the very least 30min - that's WAY above
the range for acceptable clock-drift on servers.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services