Hi Botond, I'm under the impression that the leader only loads the
database twice when it is bootstrapping. In QuorumPeer.start(), we
call loadDataBase(). The second time corresponds to the call to
zk.loadData in Leader.lead(). There could be a third time if
zkDb.isInitialized() is false thought the call path lookForLeader()->
getInitLastLoggedZxid() -> getLastLoggedZxid(). I don't see how it
could be false, though.
After we get into the main QuorumPeer loop (in run()), we only call
loadDataBase() through lookForLeader() upon calling
getInitLastLoggedZxid() -> getLastLoggedZxid(). loadDataBase() is only
executed if zkDb.isInitialized() is false, and I actually don't see a
case in which it would be true once for the call coming from
lookForLeader().
The part I can't remember is why we need to call loadData() in
Leader.lead() in the case that the data tree has been initialized
already. If we are somehow skipping it when it has been initialized
already, then I missed it. I'll keep looking into it...
-Flavio
On Dec 13, 2011, at 11:55 AM, Botond Hejj wrote:
Thanks Camille,
Sorry, my assumption was wrong. I've made now a test and indeed the
session doesn't expire in this case.
This means than the only problem is that the service is down for an
increasing amount of time if snapshot is increasing. We use SAN to
store the snapshot and reading it back twice during leader election
can be a little slow (~30 secs). It is not bad at all but still have
anybody tried making the leader election faster in this case?
Regards,
Botond
On Mon, Dec 12, 2011 at 18:35, Camille Fournier <[email protected]>
wrote:
Existing sessions will not expire from the server side during
election.
Your client code may choose to close them on its end if you sit in a
DISCONNECTED state for too long, but nothing should be expiring the
sessions while quorum is not available.
C
On Mon, Dec 12, 2011 at 12:06 PM, Botond Hejj <[email protected]
wrote:
Hi ZooKeeper users,
I am playing currently with zookeeper and testing what happens if
the
leader of an ensemble goes down.
I know that during the leader election zookeeper server won't
reply to
any requests and if leader election takes a long time than existing
sessions might expire.
What I see in my tests that each server reads the last snapshot file
to get last zxid for leader election and when the leader is elected
than the leader reads the snapshot again before it syncs the
followers.
This means that the more data we store in zookeeper the longer it
takes to elect a new leader. This is also means as load of the
ensemble increases clients need bigger session timeout to "survive"
the loss of the leader.
Is it possible to do anything about this and have a fast leader
election even if the snapshot is big?
Regards,
Botond Hejj
--
Botond Hejj
Morgan Stanley | Technology
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Phone: +36 1 881-3962
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flavio
junqueira
research scientist
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