Eric,
Thanks for the information. I didn't realize that Sequoia only ran
synchronously, although now that I think about it, it somewhat makes sense.
Would there be any way to get Sequoia to work async? My goal is not
necessarily to have a high-availability DB, but rather a real-time backup.
Consequently, if my remote writes are slightly delayed, I could live with
it. Otherwise, I agree, the performance would really be lacklustre, as some
writes are large, and the remote connections aren't always speedy.
Just to clarify the meaning of synchronous:
Sequoia does not have to wait for all backends to complete before
returning the result to the client (you can tune the WaitForCompletion
policy in the load balancer element to return as soon as the first
backend has successfully completed).
Now when we need to take a checkpoint for backup/restore/enable/disable
operations, we need to fully synchronize all backends to be sure that
all writes are flushed on all backends.
In general, each backend runs independently and processes the queries in
the same total order as the others but they do not run in a global
synchronous execution (even though this is the illusion that is provided
to the client). Behind the scenes, backends execute asynchronously.
Hope this clarifies the discussion,
Emmanuel
--
Emmanuel Cecchet
Chief Architect, 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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