Leander,
The first setup (sequoia1.png) uses one active Sequoia controller at any
time, which controls the RAIDb-1 over the two DB servers. The other
controller is stand-by. If the DB01server, or the DB01 Sequoia controller
fails, something like Heartbeat will switch DB01's IP address to the DB02
server and start up the Sequoia controller on DB02.
I would not recommend that option. In case of a controller failure, your
databases could not be in the same state and controller2 would have to
way to detect it. Moreover, you would have to alter your datasource
definitions in Tomcat to point to the new controller. The downtime would
probably be significant in case of failure.
The second setup (sequoia2.png) uses two active Sequoia controllers
(under normal circumstances), which both control a single database
instance. The Sequoia/JDBC connection string should now list two
Sequoia controller backends, I suppose?
Yes you are absolutely right.
The RAIDb-1 is now achieved
by communication between the two controllers, so every (write-)query will
be replicated by sending it from one controller to the other. Is this
even
possible?
Yes, it has been designed exactly for that purpose.
And what will happen if one of the controllers/databases fails?
If one controller fails, the driver contains transparent failover code
and will automatically reconnect, retrieve the transactional context on
the remaining controller, retrieve the query result if the controller
crashed after the query was sent or automatically retry the query if the
1st controller crashed before the 2nd received it. If a database fail,
controllers transparently retry the query (if it is a read) or retrieve
the result from the other backend (if it is a write).
In all cases, the application will never see a SQLException, everything
is transparently handled (as long as you have at least 1
controller/backend up and running).
Will the Sequoia JDBC driver notice this and redirect all queries to the
remaining controller?
Yes.
Thanks for your interest in Sequoia,
Emmanuel
--
Emmanuel Cecchet
Chief Scientific Officer, Continuent
Blog: http://emanux.blogspot.com/
Open source: http://www.continuent.org
Corporate: http://www.continuent.com
Skype: emmanuel_cecchet
Cell: +33 687 342 685
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