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From Patrick Hunt <ph...@apache.org>
Subject Re: Discover LEADER from JMX
Date Wed, 09 May 2018 18:23:31 GMT
iiuc what you are interested in the information is already available. The
beans have a "state" attribute which indicates following vs leading.

Try attaching a jconsole to the running servers, use the "mbeans" tab and
open org.apache.ZooKeeperService -> replicatedserver -> replica ->
attributes, you'll see the "state" attribute there.

Patrick

On Wed, May 9, 2018 at 8:02 AM, Enrico Olivelli <eolivelli@gmail.com> wrote:

> Thank you Edward
>
> I will pack all together and send out a patch as soon as I have time.
> I am running 3.5 in production and given than an RC for 3.5.4 is going to
> be cut soon I will have to wait for 3.5.5 and I assume it won't be
> immediate.
>
> Cheers
> Enrico
>
> Il giorno mer 9 mag 2018 alle ore 14:37 Edward Ribeiro <
> edward.ribeiro@gmail.com> ha scritto:
>
> > Sent before finishing the previous email. Only to complement, the
> > findLeader() could have been as below, but this change is only a nitty
> > detail and totally irrelevant to the questions you are asking. :)
> >
> > /**
> >  * Returns the address of the node we think is the leader.
> >  */
> > protected QuorumServer findLeader() {
> >
> >     // Find the leader by id
> >     long currentLeader = self.getCurrentVote().getId();
> >
> >     QuorumServer leaderServer = self.getView().get(currentLeader);
> >
> >     if (leaderServer == null) {
> >         LOG.warn("Couldn't find the leader with id = {}", currentLeader);
> >     }
> >     return leaderServer;
> > }
> >
> > Edward
> >
> > On Wed, May 9, 2018 at 9:29 AM, Edward Ribeiro <edward.ribeiro@gmail.com
> >
> > wrote:
> >
> > > Hi Enrico,
> > >
> > > Well, I am not an expert on QuorumPeer either (not an expert on
> anything,
> > > really), but maybe it's the variable and method below?
> > >
> > > ----------------- QuorumPeer ------------------
> > >
> > > /**
> > >  * This is who I think the leader currently is.
> > >  */
> > > volatile private Vote currentVote;
> > >
> > > public synchronized Vote getCurrentVote(){
> > >     return currentVote;
> > > }
> > >
> > > ---------------------------------------
> > >
> > >
> > > Then it's a matter of calling quorumPeer.getCurrentVote().getId() and
> > > quorumPeer.getServerState()?
> > >
> > > Btw, the Learner class has this handy method below (self is a
> > QuorumPeer):
> > >
> > > ---------------- Learner --------------------
> > >
> > > /**
> > >  * Returns the address of the node we think is the leader.
> > >  */
> > > protected QuorumServer findLeader() {
> > >     QuorumServer leaderServer = null;
> > >     // Find the leader by id
> > >     Vote current = self.getCurrentVote();
> > >     for (QuorumServer s : self.getView().values()) {
> > >         if (s.id == current.getId()) {
> > >             leaderServer = s;
> > >             break;
> > >         }
> > >     }
> > >     if (leaderServer == null) {
> > >         LOG.warn("Couldn't find the leader with id = "
> > >                 + current.getId());
> > >     }
> > >     return leaderServer;
> > > }
> > >
> > > ---------------------------------------
> > >
> > > By the way, as a side note, the map traversal could be changed by:
> > >
> > > ----------------------------
> > >
> > > if (self.getView().contains(current.getId()) {
> > >
> > > }
> > >
> > > ---------------------------
> > >
> > >
> > >
> > > You can see above this method the quorumPeer.getView() returns a
> Map<sid,
> > > QuorumServer> as below:
> > >
> > > -------------QuorumPeer ---------
> > >
> > > /**
> > >  * A 'view' is a node's current opinion of the membership of the entire
> > >  * ensemble.
> > >  */
> > > public Map<Long,QuorumPeer.QuorumServer> getView() {
> > >     return Collections.unmodifiableMap(getQuorumVerifier().
> > > getAllMembers());
> > > }
> > >
> > > -----------------------------
> > >
> > >
> > > And then it retrieves the QuorumServer that has many more information
> > > about the node besides the sid (InetSocketAddress, hostname, etc). :)
> > >
> > >
> > > Cheers,
> > > Edward
> > >
> > > On Wed, May 9, 2018 at 8:50 AM, Enrico Olivelli <eolivelli@gmail.com>
> > > wrote:
> > >
> > >> So I am trying to create a patch in order to expose on JMX the id of
> the
> > >> current "leader" (on the JVM of a follower)
> > >>
> > >> I am trying to find in ZK which is the variable which holds the ID of
> > the
> > >> current leader.
> > >> I am new to the internal of QuorumPeer
> > >>
> > >> Can someone give me some hint ?
> > >>
> > >> Enrico
> > >>
> > >> Il giorno mar 8 mag 2018 alle ore 10:08 Ansel Zandegran <
> > >> Ansel.Zandegran@infor.com> ha scritto:
> > >>
> > >> > Hi,
> > >> > That is possible with 4 letter commands. We are using it now. In
> 3.5.x
> > >> it
> > >> > is going to be removed in favour of admin server (embedded web
> > server).
> > >> > We are running in an environment where it’s not possible to run
JMX
> or
> > >> > embedded web servers.
> > >> >
> > >> > So I am wondering if there is another way? It would be nice to have
> > this
> > >> > info as a znode.
> > >> >
> > >> > Best regards,
> > >> > Ansel
> > >> >
> > >> > > On 8 May 2018, at 09:55, Flavio Junqueira <fpj@apache.org>
wrote:
> > >> > >
> > >> > > Hi Enrico,
> > >> > >
> > >> > > You can determine the state of a server it via 4-letter commands.
> > >> Would
> > >> > that work for you?
> > >> > >
> > >> > > -Flavio
> > >> > >
> > >> > >> On 8 May 2018, at 09:09, Enrico Olivelli <eolivelli@gmail.com>
> > >> wrote:
> > >> > >>
> > >> > >> Hi,
> > >> > >> is there any way to see in JMX which is the leader of a ZooKeeper
> > >> > cluster?
> > >> > >>
> > >> > >> My problem is: given access to any of the nodes of the cluster
I
> > >> want to
> > >> > >> know from JMX which is the current leader.
> > >> > >> It seems to me that this information is not available, you
can
> know
> > >> > only if
> > >> > >> the local node is Leader or Follower.
> > >> > >>
> > >> > >> Cheers
> > >> > >> Enrico
> > >> > >
> > >> >
> > >> >
> > >>
> > >
> > >
> >
>

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