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From Jordan Zimmerman <jor...@jordanzimmerman.com>
Subject Re: question about curator - retry policy
Date Fri, 20 May 2016 21:43:24 GMT
If you are using Curator’s Service Discovery code, it will be continuously re-trying the
connections. This is not because of the retry policy it’s because the Service Discovery
code manages connection interruptions internally.

-Jordan

> On May 20, 2016, at 4:40 PM, Moshiko Kasirer <moshek@liveperson.com> wrote:
> 
> Thanks for the replay I will send those logs ASAP.
> It's difficult to understand the connection mechanism of zk ....
> We are using curator 2.10 as our service discovery so we have to make sure that when
zk is alive we connect and inform the our server is up we do that by listening to curator
connection listener which I think has also to do with the retry policy.... But what I can't
understand is why sometimes we can see in the log that curator gave up (Lost) yet still a
second later curator connection is restored how? Is it because zk session heartbeat restored
the connection? Does that Iovine curator to change his connection state? And on the other
side we sometimes get to a point were zk is up but curator connection stays as Lost...
> That is why I thought of using the new always try policy you entered do you think it
can help? That why  hope there will be no way that zk is up but curator status is lost.....as
once he will retry he will reconnect to zk.... Is that correct?
> 
> בתאריך 21 במאי 2016 00:10,‏ "Jordan Zimmerman" <jordan@jordanzimmerman.com
<mailto:jordan@jordanzimmerman.com>> כתב:
> Curator’s retry policies are used within each CuratorFramework operation. For example,
when you call client.setData().forPath(p, b) the retry policy will be invoked if there is
a retry-able exception during the operation. In addition to the retryPolicy, there are connection
timeouts. The behavior of how this is handled changed between Curator 2.x and Curator 3.x.
In Curator 2.x, for every iteration of the retry, the operation will wait until connection
timeout when there’s no connection. In Curator 3.x, the connection timeout wait only occurs
once (if the default ConnectionHandlingPolicy is used).
> 
> In any event, ZooKeeper itself tries to maintain the connection. Also, Curator will re-create
the internally managed connection depending various network interruptions, etc. I’d need
to see the logs to give you more input. 
> 
> -Jordan
> 
>> On May 19, 2016, at 10:12 AM, Moshiko Kasirer <moshek@liveperson.com <mailto:moshek@liveperson.com>>
wrote:
>> 
>> first i would like to thank you about curator we are using it as part of our service
discovery 
>> 
>> solution and it helps a lot!! 
>> 
>> i have a question i hope you will be able to help me with. 
>> 
>> its regarding the curator retry policy it seems to me we dont really understand when
this policy is 
>> 
>> invoked,  as i see in our logs that although i configured it as max retry 1 actually
in the logs i see 
>> 
>> many ZK re connection attempts (and many curator gave up messages but later i see

>> 
>> reconnected status...) . is it possible that that policy is only relevant to manually
invoked 
>> 
>> operations against the ZK cluster done via curator ? and that the re connections
i see in the logs 
>> 
>> are caused by the fact that the ZK was available during start up so sessions were
created and 
>> 
>> then when ZK was down the ZK clients (not curator)  are sending heartbeats as part
of the ZK 
>> 
>> architecture? that is the part i am failing to understand and i hope you can help
me with that.
>> 
>> you have recently added RetreyAllways policy and i wanted to know if it is save to
use it? 
>> 
>> the thing is we always want to retry to reconnect to ZK when he is available but
that is something 
>> 
>> the ZK client does as long as he has open sessions right?  i am not sure that it
has to do with the 
>> 
>> retry policy ... 
>> 
>> thanks,
>> 
>> moshiko
>> 
>> -- 
>> 
>> Moshiko Kasirer
>> Software Engineer
>> T: +972-74-700-4357 <tel:%2B972-74-700-4357>
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