Emmanuel Cecchet wrote:
Jamin wrote:
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.
Yet this is what the Sequoia User's Guide talks about for a fault
tolerant Recovery Log. From section 7.5.3,
http://sequoia.continuent.org/doc/2.10/userGuide/ar01s07.html#N10809:
"it is possible to make the recovery log fault tolerant by redirecting
it to a Sequoia controller (even self) that will distribute and
replicate the log content on several backends."
However your previous statement:
> 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).
seems to indicate that simply having multiple Sequoia controllers will
automatically provide fault tolerance of the Recovery Log.
Where should these Recovery Log databases be stored? If they are stored
on the MySQL backends I still see them running the same problem when one
of the backends fails. Are you instead suggesting that the Recovery Log
be stored on the controller? If so, would this result in each
controller having its own independent copy of the Recovery Log? Also,
is there a suggested backend to use for the storage?
I'm sorry if it seems I'm missing something obvious, but the
documentation really doesn't make this very clear. In fact it seems to
contradict what you're saying (as indicated above).
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
That documentation link appears to be for 3.x, whereas the latest stable
release (according to the website) is 2.10.9 which is what I've been
trying to use.
--
Jamin W. Collins
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