On Thu, Apr 22, 2004 at 09:42:12AM -0400, Eric Comeau wrote:
>
> What is Oracle selling as their replication solution these days?
[. . .]
> Their ORAC if I understand it correctly is a "cluster" solution and
> no a "replication" solution.
This is an example of why I think most of the discussion about
"replication" is so confusing. ORAC is certainly a kind of
replication: it provides always-on, hot redundancy in a cluster of
machines. It's multi-master, and something very close to
asynchronous. It's a _very_ clever system, but it'll do you not one
whit of good if your primary site fails. Also, it's not suitable for
use on unreliable hardware: every cluster member failure causes a
"remastering" event which causes everything to stop while remastering
happens. Finally, it requires some nifty but expensive storage --
storage which itself could be a single point of failure, if it failed
in the right ways.
To solve all of that, Oracle also offers Data Guard. This is
basically a standard log-shipping technique. The off-site "standby"
databases can't be used while in standby mode. This has all the
standard caveats of asynchronous WAN replication, not least of which
is that if you processed a $100 million transaction right before your
master failed, and then you recovered onto a slave which didn't have
that last moment of data, you might find yourself making a $100
million mistake.
So, Oracle Corp offers two different ways to keeo you up nights. :)
I'm sure they're both wonderful products. But they certainly don't
have a one-size-fits-all approach.
A
--
Andrew Sullivan | ajs@crankycanuck.ca
