Jamin,
I guess I'm still not seeing how the RecoveryLog avoids being point of
failure. I've looked through the three guides (Administration,
Installation, and User) but fail to see where this is clarified.
Right now I have two MySQL servers (let's call them M1 and M2) and a
single Sequoia server (let's call it S1) with a virtual database (V1)
comprised of both MySQL servers.
That's your problem, as you have a single Sequoia controller S1, you
will have only 1 recovery log and they are both a single point of
failure. This is why you need to replicate the controller (and as there
is one recovery log per virtual database per controller, you will also
replicate the recovery log).
If I'm understanding correctly for the RecoveryLog to be fault
tolerant it would need to be pointed to yet another virtual database
(V2) which would need to be on at least two servers. Assuming I put
it on M1 and M2, then when either M1 or M2 fail the RecoveryLog would
become degraded and need to be recovered just like the original
virtual database (V1) would it not?
This is not really useful since as soon as you lose the controller, the
recovery log becomes useless.
If this is covered in the documentation, perhaps someone could point
me to what I've missed?
The documentation assumes upfront that you are replicating the
controllers if you want availability.
This is probably hidden somewhere in the basic concepts part like in
http://sequoia.continuent.org/doc/infocenter/index.jsp?topic=/org.continuent.sequoia.doc/html/Sequoia_URL_options.html
I wanted to get a grasp of how to avoid what I perceive as a single
point of failure in the RecoveryLog before proceeding with what seems
to be a more complex configuration.
The controller/recovery log replication is tightly coupled so one cannot
go without the other. This is why we want to make the recovery log
mandatory by default in Sequoia 4.
Hope this helps,
Emmanuel
--
Emmanuel Cecchet - Research scientist
EPFL - LABOS/DSLAB - IN.N 317
Phone: +41-21-693-7558
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