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Zookeeper >> mail # user >> Serious problem processing hearbeat on login stampede


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Re: Serious problem processing hearbeat on login stampede
chang,

if the problem is on client startup, then it isn't the heartbeat
stamped, it is session establishment. the heartbeats are very light
weight, so i can't imagine them causing any issues.

the two key issues we need to know are: 1) the version of the server
you are running, and 2) if you are using a dedicated device for the
transaction log.

ben

2011/4/14 Patrick Hunt <[EMAIL PROTECTED]>:
> 2011/4/14 Chang Song <[EMAIL PROTECTED]>:
>>> 2) regarding IO, if you run 'iostat -x 2' on the zk servers while your
>>> issue is happening, what's the %util of the disk? what's the iowait
>>> look like?
>>>
>>
>> Again, no I/O at all.   0%
>>
>
> This is simply not possible.
>
> Sessions are persistent. Each time a session is created, and each time
> it is closed, a transaction is written by the zk server to the data
> directory. Additionally log4j based logs are also being streamed to
> the disk. Each of these activities will cause disk IO that will show
> up on iostat.
>
>> Patrick. They are not continuously login/logout.
>> Maybe a couple of times a week. and before they push new feature.
>> When this happens, clients in group A drops out of clusters, which causes
>> problem to other unrelated services.
>>
>
> Ok, good to know.
>
>>
>> It is not about use case, because ZK clients simply tried to connect to
>> ZK ensemble. No use case applies. Just many clients login at the
>> same time or expires at the same time or close session at the same time.
>>
>
> As I mentioned, I've seen cluster sizes of 10,000 clients (10x what
> you report) that didn't have this issue. While bugs might be lurking,
> I've also worked with many teams deploying clusters (probably close to
> 100 by now), some of which had problems, the suggestions I'm making to
> you are based on that experience.
>
>> Heartbeats should be handled in an isolated queue and a
>> dedicated thread.  I don't think we need strict ordering keeping
>> of heartbeats, do we?
>
> ZK is purposely architected this way, it is not a mistake/bug. It is a
> falicy for a highly available service to respond quickly to a
> heartbeat when it cannot service regular requests in a timely fashion.
> This is one of the main reasons why heartbeats are handled in this
> way.
>
> Patrick
>
>>> Patrick
>>>
>>>> It's about CommitProcessor thread queueing (in leader).
>>>> QueuedRequests goes up to 800, so does commitedRequests and
>>>> PendingRequestElapsedTime. PendingRequestElapsedTime
>>>> goes up to 8.8 seconds during this flood.
>>>>
>>>> To exactly reproduce this scenario, easiest way is to
>>>>
>>>> - suspend All JVM client with debugger
>>>> - Cause all client JVM OOME to create heap dump
>>>>
>>>> in group B. All clients in group A will not be able to receive
>>>> ping response in 5 seconds.
>>>>
>>>> We need to fix this as soon as possible.
>>>> What we do as a workaround is to raise sessionTimeout to 40 sec.
>>>> At least clients in Group A survives. But this increases
>>>> our cluster failover time significantly.
>>>>
>>>> Thank you, Patrick.
>>>>
>>>>
>>>> ps. We actually push ping request to FinalRequestProcessor as soon
>>>>     as the packet identifies itself as ping. No dice.
>>>>
>>>>
>>>>
>>>> 2011. 4. 14., 오전 12:21, Patrick Hunt 작성:
>>>>
>>>>> Hi Chang, it sounds like you may have an issue with your cluster
>>>>> environment/setup, or perhaps a resource (GC/mem) issue. Have you
>>>>> looked through the troubleshooting guide?
>>>>> https://cwiki.apache.org/confluence/display/ZOOKEEPER/Troubleshooting
>>>>>
>>>>> In particular 1000 clients connecting should be fine, I've personally
>>>>> seen clusters of 7-10 thousand clients. Keep in mind that each session
>>>>> establishment is essentially a write (so the quorum in involved) and
>>>>> what we typically see there is that the cluster configuration has
>>>>> issues. 14 seconds for a ping response is huge and indicates one of
>>>>> the following may be an underlying cause:
>>>>>
>>>>> 1) are you running in a virtualized environment?
>>>>> 2) are you co-locating other services on the same host(s) that make up