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From: Sameer Kumar <[email protected]>
To: Bill Moran <[email protected]>
Cc: Thomas Harold <[email protected]>
Cc: Albe Laurenz <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: PG replication across DataCenters
Date: Mon, 30 Dec 2013 02:13:44 +0800
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>
> What I don't see streaming working for is DR drills.  I need to, in a
> controlled manner, move the entire application to the secondary datacenter,
> while keeping all the nodes in sync, make sure everything operates properly
> from there (which means allowing database updates), then move it all back
> to the primary datacenter, without losing sync on any slaves (this is a 2T
> database, which I'm sure isn't the largest anyone has dealt with, but it
> means that reseeding slaves is a multi-hour endeavour).  With Slony, these
> drills are easy: a single slonik command relocates the master to the DR
> datacenter while keeping everything in sync, and when testing is complete,
> another slonik command puts everything back the way it was, without any
> data loss and with minimal chance for human error.


I guess I got your point :)
Agree to you now! :)
With v9.3 I think I would be easy to swap the roles for primary and DR. (I
need to test this before I can say for sure).

But still it will be a pain if one needs to shift all the operations to DR
(which is a a valid case, e.g. you would do that for testing the readiness
of your DR site by doing a mock failover) and then shift back to Primary
Site (assuming while operations were going on on DR site, primary site was
kept down purposefully). This will involve taking a backup from DR to
primary and then swapping the roles.
I guess this limitation will be soon waived off. I guess v9.4 or next one
should have this feature (no backups as long as your wal_keep_segment is
high enough to cater to your testing/mock failover window).

I agree slonik and few other utilities/tool around it
administration/management is quite easy.


If you feel that the current implementation of streaming replication is
> able to do that task, then I'll have to move up my timetable to re-evaluate
> it.  It _has_ been a few versions since I've taken a good look at it.


Given your expectation above, v9.3 is a good candidate. But you can afford
to give it a miss.
You must try once v9.4 is out.


Regards
Sameer
Ashnik Pte. Ltd.
Singapore


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