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Date: Tue, 25 Aug 2015 09:18:17 +0300
Message-ID: 
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Subject: Re: The solution to the sporadic connection refused exceptions
From: abdullah alamoudi <bamousaa@gmail.com>
To: dev@asterixdb.incubator.apache.org
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Thanks Raman,
I already figured that out. I am currently looking into synchronization
(Even though I don't need it right now) but it can definitely become handy
in future tasks.

Cheers,
Abdullah.

P.S
Using ZooKeeper seems the cleaner/easier approach. Thanks for bringing this
up :-)

On Tue, Aug 25, 2015 at 9:06 AM, Raman Grover <ramangrover29@gmail.com>
wrote:

> Abdullah, Zookeeper allows setting up a  "watch" on any node (recall that
> internally zookeeper maintains info as a tree of nodes, called znodes).
> Check out the zookeeper API here
> <
> http://zookeeper.apache.org/doc/trunk/zookeeperProgrammers.html#ch_zkWatches
> >.
> Watch nodes are a common mechanism for notifying changes to information
> stored within a node, creation/deletion of a child under the node or
> deletion of node.
> One can attach listeners and be notified.
>
>
> Regards,
> Raman
>
> On Mon, Aug 24, 2015 at 9:47 PM, abdullah alamoudi <bamousaa@gmail.com>
> wrote:
>
> > @Raman,
> > I will look into doing it with Zookeeper.
> >
> > Is there a way to notify Managix once the cluster state has been updated
> in
> > Zookeeper? or would Managix have to poll and check the state?
> >
> > Cheers,
> > Abdullah.
> >
> > On Tue, Aug 25, 2015 at 3:28 AM, Raman Grover <ramangrover29@gmail.com>
> > wrote:
> >
> > > Well, the state of an instance (and metadata including configuration)
> is
> > > kept in Zookeeper instance that is accessible to Managix and CC. CC
> > should
> > > be able to set the state of the cluster in Zookeeper under the right
> > znode
> > > which can viewed by Managix.
> > >
> > > There exists a communication channel for CC and Managix to share
> > > information on state etc. I am not sure if we need another channel such
> > as
> > > RMI between Managix and CC.
> > >
> > > Regards,
> > > Raman
> > >
> > >
> > >
> > > On Mon, Aug 24, 2015 at 12:58 PM, abdullah alamoudi <
> bamousaa@gmail.com>
> > > wrote:
> > >
> > > > Well, it depends on your definition of the boundaries of managix.
> What
> > I
> > > > did is that I added an RMI object in the InstallerDriver which
> > basically
> > > > listen for state changes from the cluster controller. This means some
> > > > additional logic in the CCApplicationEntryPoint where after the CC is
> > > > ready, it contacts the InstallerDriver using RMI and at that point
> > only,
> > > > the InstallerDriver can return to managix and tells it that the
> startup
> > > is
> > > > complete.
> > > >
> > > > Not sure if this is the right way to do it but it definitely is
> better
> > > than
> > > > what we currently have.
> > > > Abdullah.
> > > >
> > > > On Mon, Aug 24, 2015 at 10:00 PM, Chris Hillery
> <chillery@hillery.land
> > >
> > > > wrote:
> > > >
> > > > > Hopefully the solution won't involve additional important logic
> > inside
> > > > > Managix itself?
> > > > >
> > > > > Ceej
> > > > > aka Chris Hillery
> > > > >
> > > > > On Mon, Aug 24, 2015 at 7:26 AM, abdullah alamoudi <
> > bamousaa@gmail.com
> > > >
> > > > > wrote:
> > > > >
> > > > > > That works but it doesn't feel right doing it this way. I am
> going
> > to
> > > > fix
> > > > > > this one for good.
> > > > > >
> > > > > > Cheers,
> > > > > > Abdullah.
> > > > > >
> > > > > > On Mon, Aug 24, 2015 at 5:11 PM, Ian Maxon <imaxon@uci.edu>
> wrote:
> > > > > >
> > > > > > > The way I assured liveness for the YARN installer was to try
> > > running
> > > > > "for
> > > > > > > $x in dataset Metadata.Dataset return $x" via the API. I just
> > > polled
> > > > > for
> > > > > > a
> > > > > > > reasonable amount of time  (though honestly, thinking about it
> > now,
> > > > the
> > > > > > > correct parameter to use for the polling interval is the
> startup
> > > wait
> > > > > > time
> > > > > > > in the parameters file :) ). It's not perfect, but it gives
> less
> > > > false
> > > > > > > positives than just checking ps for processes that look like
> > > CCs/NCs.
> > > > > > >
> > > > > > > - Ian.
> > > > > > >
> > > > > > > On Mon, Aug 24, 2015 at 5:03 AM, abdullah alamoudi <
> > > > bamousaa@gmail.com
> > > > > >
> > > > > > > wrote:
> > > > > > >
> > > > > > > > Now that I think about it. Maybe we should provide multiple
> > ways
> > > to
> > > > > do
> > > > > > > > this. A polling mechanism to be used for arbitrary time and a
> > > > pushing
> > > > > > > > mechanism on startup.
> > > > > > > > I am going to start implementation of this and will probably
> > use
> > > > RMI
> > > > > > for
> > > > > > > > this task both ways (CC to InstallerDriver and
> InstallerDriver
> > to
> > > > > CC).
> > > > > > > >
> > > > > > > > Cheers,
> > > > > > > > Abdullah.
> > > > > > > >
> > > > > > > > On Mon, Aug 24, 2015 at 2:19 PM, abdullah alamoudi <
> > > > > bamousaa@gmail.com
> > > > > > >
> > > > > > > > wrote:
> > > > > > > >
> > > > > > > > > So after further investigation, turned out our startup
> > process
> > > > just
> > > > > > > > starts
> > > > > > > > > the CC and NC processes and then make sure the processes
> are
> > > > > running
> > > > > > > and
> > > > > > > > if
> > > > > > > > > the processes were found to be running, it returns the
> state
> > of
> > > > the
> > > > > > > > cluster
> > > > > > > > > to be active and the subsequent test commands can start
> > > > > immediately.
> > > > > > > > >
> > > > > > > > > This means that the CC could've started but is not yet
> ready
> > > when
> > > > > we
> > > > > > > try
> > > > > > > > > to process the next command. To address this, we need a
> > better
> > > > way
> > > > > to
> > > > > > > > tell
> > > > > > > > > when the startup procedure has completed. we can do this by
> > > > pushing
> > > > > > (CC
> > > > > > > > > informs installer driver when the startup is complete) or
> > > polling
> > > > > > (The
> > > > > > > > > installer driver needs to actually query the CC for the
> state
> > > of
> > > > > the
> > > > > > > > > cluster).
> > > > > > > > >
> > > > > > > > > I can do either way so let's vote. My vote goes to the
> > pushing
> > > > > > > mechanism.
> > > > > > > > > Thoughts?
> > > > > > > > >
> > > > > > > > > On Mon, Aug 24, 2015 at 10:15 AM, abdullah alamoudi <
> > > > > > > bamousaa@gmail.com>
> > > > > > > > > wrote:
> > > > > > > > >
> > > > > > > > >> This solution turned out to be incorrect. Actually, the
> test
> > > > cases
> > > > > > > when
> > > > > > > > I
> > > > > > > > >> build after using the join method never fails but running
> an
> > > > > actual
> > > > > > > > asterix
> > > > > > > > >> instance never succeeds which is quite confusing.
> > > > > > > > >>
> > > > > > > > >> I also think that the startup script has a major bug where
> > it
> > > > > might
> > > > > > > > >> returns before the startup is complete. More on this
> > > later......
> > > > > > > > >>
> > > > > > > > >> On Mon, Aug 24, 2015 at 7:48 AM, abdullah alamoudi <
> > > > > > > bamousaa@gmail.com>
> > > > > > > > >> wrote:
> > > > > > > > >>
> > > > > > > > >>> It is highly unlikely that it is related.
> > > > > > > > >>>
> > > > > > > > >>> Cheers,
> > > > > > > > >>> Abdullah.
> > > > > > > > >>>
> > > > > > > > >>> On Mon, Aug 24, 2015 at 5:45 AM, Chen Li <
> chenli@gmail.com
> > >
> > > > > wrote:
> > > > > > > > >>>
> > > > > > > > >>>> @Abdullah: Is this issue related to
> > > > > > > > >>>> https://issues.apache.org/jira/browse/ASTERIXDB-1074?
> Ian
> > > > and I
> > > > > > > plan
> > > > > > > > to
> > > > > > > > >>>> look into the details on Monday.
> > > > > > > > >>>>
> > > > > > > > >>>> On Sun, Aug 23, 2015 at 10:08 AM, abdullah alamoudi <
> > > > > > > > bamousaa@gmail.com
> > > > > > > > >>>> >
> > > > > > > > >>>> wrote:
> > > > > > > > >>>>
> > > > > > > > >>>> > About 3-4 days ago, I was working on the addition of
> the
> > > > > > > filesystem
> > > > > > > > >>>> based
> > > > > > > > >>>> > feed adapter and it didn't take anytime to complete.
> > > > However,
> > > > > > > when I
> > > > > > > > >>>> wanted
> > > > > > > > >>>> > to build and make sure all tests pass, I kept getting
> > > > > > > > >>>> ConnectionRefused
> > > > > > > > >>>> > errors which caused the installer tests to fail every
> > now
> > > > and
> > > > > > > then.
> > > > > > > > >>>> >
> > > > > > > > >>>> > I knew the new change had nothing to do with this
> > failure,
> > > > > yet,
> > > > > > I
> > > > > > > > >>>> couldn't
> > > > > > > > >>>> > direct my attention away from this bug (It just
> bothered
> > > me
> > > > so
> > > > > > > much
> > > > > > > > >>>> and I
> > > > > > > > >>>> > knew it needs to be resolved ASAP). After wasting
> > > countless
> > > > > > > hours, I
> > > > > > > > >>>> was
> > > > > > > > >>>> > finally able to figure out what was happening :-)
> > > > > > > > >>>> >
> > > > > > > > >>>> > In the startup routine, we start three Jetty web
> servers
> > > > (Web
> > > > > > > > >>>> interface
> > > > > > > > >>>> > server, JSON API server, and Feed server). Sometime
> ago,
> > > we
> > > > > used
> > > > > > > to
> > > > > > > > >>>> end the
> > > > > > > > >>>> > startup call before making sure the server.isStarted()
> > > > method
> > > > > > > > returns
> > > > > > > > >>>> true
> > > > > > > > >>>> > on all servers. At that time, I introduced the
> > > > > > > waitUntilServerStarts
> > > > > > > > >>>> method
> > > > > > > > >>>> > to make sure we don't return before the servers are
> > ready.
> > > > > > Turned
> > > > > > > > >>>> out, that
> > > > > > > > >>>> > was an incorrect way to handle this (We can blame
> > > > > stackoverflow
> > > > > > > for
> > > > > > > > >>>> this
> > > > > > > > >>>> > one!) and it is not enough that the server isStarted()
> > > > returns
> > > > > > > true.
> > > > > > > > >>>> The
> > > > > > > > >>>> > correct way to do this is to call the server.join()
> > method
> > > > > after
> > > > > > > the
> > > > > > > > >>>> > server.start().
> > > > > > > > >>>> >
> > > > > > > > >>>> > See:
> > > > > > > > >>>> >
> > > > > > > > >>>>
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> http://stackoverflow.com/questions/15924874/embedded-jetty-why-to-use-join
> > > > > > > > >>>> >
> > > > > > > > >>>> > This was equally satisfying as it was frustrating and
> > you
> > > > are
> > > > > > > > welcome
> > > > > > > > >>>> for
> > > > > > > > >>>> > the future time I saved each of you :)
> > > > > > > > >>>> > --
> > > > > > > > >>>> > Amoudi, Abdullah.
> > > > > > > > >>>> >
> > > > > > > > >>>>
> > > > > > > > >>>
> > > > > > > > >>>
> > > > > > > > >>>
> > > > > > > > >>> --
> > > > > > > > >>> Amoudi, Abdullah.
> > > > > > > > >>>
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >>
> > > > > > > > >> --
> > > > > > > > >> Amoudi, Abdullah.
> > > > > > > > >>
> > > > > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > --
> > > > > > > > > Amoudi, Abdullah.
> > > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > --
> > > > > > > > Amoudi, Abdullah.
> > > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > Amoudi, Abdullah.
> > > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Amoudi, Abdullah.
> > > >
> > >
> > >
> > >
> > > --
> > > Raman
> > >
> >
> >
> >
> > --
> > Amoudi, Abdullah.
> >
>
>
>
> --
> Raman
>


-- 
Amoudi, Abdullah.

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