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From John Nagro <>
Subject Re: ZooKeeper Session Expiration
Date Tue, 01 May 2012 13:14:56 GMT
Flavio -

We're trying to get to the bottom of it. As I understand it, in a properly
configured and operating Zk Cluster we should never see a session
expiration exception. Globally (including all systems) we see them perhaps
once a week for the last month - and it causes some issues in our system.
We saw one last night, and bookkeeper had an issue a couple days ago.

We do have a lot of nodes connecting to zookeeper for various things. We
have a home-built configuration management tool that uses zk as the data
store, the bookkeeper stuff obviously does, my coordination on top of the
bookkeeper ledgers uses it, etc. So yes, lots of machines (dozens up to
~100) talk to this zk cluster in some fashion or another - we have other
clusters too. Ultimately, more machines will talk to the configuration
stuff in the long term. I could potentially move my zk stuff off that
cluster if you think it would help.


On Tue, May 1, 2012 at 8:44 AM, Flavio Junqueira <> wrote:

> This is definitely not ideal. If you lose your zookeeper session, then
> you're not able to close your open ledgers, which will force ledger
> recovery. It is not a correctness issue, but certainly inconvenient. We
> need to fix, and I'm glad that Uma is already looking into it.
> I'm curious about why you're getting session expirations, though. Is it
> frequent or you got it once? Do you have many nodes connecting to your
> ZooKeeper instance?
> -Flavio
> On May 1, 2012, at 2:07 PM, John Nagro wrote:
> Thanks Uma - that is exactly what i am looking for. The way i am handing
> it now is to pass a bookkeeper client factory rather than an instance. When
> i encounter zk session expiration, i create a new client and discard the
> old one - getting a fresh set of connections to zk. Perhaps not idea, but
> gets the job done.
> thanks!
> -John
> On Tue, May 1, 2012 at 12:09 AM, Uma Maheswara Rao G <
> > wrote:
>>  Hi John,
>>  BK client need to handle session expire events from ZK.  Here is the
>> issue for that BOOKKEEPER-225<>
>> .
>> We will implement it soon. I hope this is your doubt. Please correct me
>> if my interpretation is wrong about your question here.
>> Thanks a lot,
>> Uma
>>  ------------------------------
>> *From:* John Nagro []
>> *Sent:* Tuesday, May 01, 2012 1:20 AM
>> *To:*
>> *Subject:* ZooKeeper Session Expiration
>>  Hello -
>>  If I start seeing ZKExceptions in the Bk Client, which appear to be due
>> to SessionExpiration errors... it seems that the BookKeeper client never
>> recovers from that? Is that correct?
>>  Thanks!
>>  -John Nagro

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