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Date: Mon, 23 Feb 2009 23:54:53 -0800
Subject: Re: Recommended session timeout
From: Mahadev Konar <mahadev@yahoo-inc.com>
To: <zookeeper-user@hadoop.apache.org>, <joey42+reply@gmail.com>
Message-ID: <C5C8E7CD.189A6%mahadev@yahoo-inc.com>
Thread-Topic: Recommended session timeout
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On 2/23/09 11:37 PM, "Joey Echeverria" <joey42@gmail.com> wrote:

> Thanks for the link to the documentation. I've been running tests with
> a 5 second session timeout and disconnect events appear frequent. The
> network they're operating on is generally quite, but the disconnects
> to correlate with an increase in activity (e.g. loading data into the
> system).
>=20
> Does this seem normal to you or does it imply a potential
> configuration problem on my network?
How many zookeeper quorum servers are you running? What is the config for
the zookeeper servers?

>=20
> On a related topic, I was reading the 3.1 client source code,
> particularly the reconnect source, and noticed that the client sleeps
> for up to 1 second before trying to reconnect. This seems excessive
> and with a 5 second session timeout leads to more frequent session
> expirations. Almost every time it sleeps for more than about 800 ms, a
> disconnect is followed by an expiration.
Can you point me to the code which you think does this? A client is suppose=
d
to disconnect itself from a server if it does not hear a response to its
ping's within 1/3 of the session timeout. It should then reconnect to the
other servers. Session expiration  happening so frequently does indicate a
problem. More information on your setup will help.

Thanks
mahadev

>=20
> Is this a bug, or desirable behavior?
>=20
> Thanks,
>=20
> -Joey
>=20
> On Mon, Feb 23, 2009 at 10:37 PM, Patrick Hunt <phunt@apache.org> wrote:
>> The latest docs (3.1.0 has some updates to that section) can be found he=
re:
>> http://hadoop.apache.org/zookeeper/docs/r3.1.0/zookeeperProgrammers.html=
#ch_z
>> kSessions
>>=20
>> Patrick
>>=20
>> Mahadev Konar wrote:
>>>=20
>>> Hi Joey,
>>> =A0here is a link to information on session timeouts.
>>>=20
>>> http://hadoop.apache.org/zookeeper/docs/r3.0.1/zookeeperProgrammers.htm=
l#ch_
>>> zkSessions
>>> =A0The session timeouts depends on how sensitive you want your applicatio=
n
>>> to
>>> be. A very low session timeout like (1-2 seconds) might lead to your
>>> application being very sensitive to events like minor network problems
>>> etc.,
>>> a higher values of say (30 seconds) on the other hand might lead to slo=
w
>>> detection of client failures -- example one of the zookeeper client whi=
ch
>>> has ephemeral node goes down, in this case the ephemeral nodes will onl=
y
>>> go
>>> away after session timeout.
>>>=20
>>> I have seen some users using 10-15 seconds of session timeout, but you
>>> should use as per your application requirements.
>>>=20
>>> Hope this helps.
>>> mahadev
>>>=20
>>>=20
>>> On 2/22/09 3:09 AM, "Joey Echeverria" <joey42@gmail.com> wrote:
>>>=20
>>>> Is there a recommended session timeout? Does it change based on the
>>>> ensemble size?
>>>>=20
>>>> Thanks,
>>>>=20
>>>> -Joey
>>>=20
>>=20