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From Patrick Hunt <ph...@apache.org>
Subject Re: Backups
Date Fri, 20 Jan 2012 17:01:46 GMT
On Thu, Jan 19, 2012 at 11:42 PM, kishore g <g.kishore@gmail.com> wrote:
> User error is a valid use case.  Are we assuming that because of user error
> the ZK is not usable at this point? if not, can some one please explain how
> having a back up can actually restore the data without bringing all zk
> servers down and not disrupting the clients.

Not sure what you mean by "zk is not usable". User error meaning
someone deleted/corrupted the cluster state at the server level and
the service cannot be started/restarted? Or just that someone messed
up the znodes via some user api operation?

re "backup/restore ... not disrupting the clients" that's not possible
via some backup type operation at the server level. The clients track
the version of the service and will not come up on a server that's
behind the zxid last seen by that client (ie no going back in time).
Doing so would invalidate all kinds of zk guarantees. Anyway, if
you're in this state you're in big trouble anyway. You can see this
today, sometime ppl will start a zk cluster and some clients, then
decide they want to wipe the znode data space, they do this by
stopping the service, wiping the datadir, and restarting. They are
then surprised when the clients (which are not restarted) cannot
reconnect to the service.

Patrick

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