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From Patrick Hunt <ph...@apache.org>
Subject Re: Misbehaving zk servers
Date Thu, 29 Apr 2010 17:24:21 GMT
Did you find any bugs on java.sun.com related to those? ;-)

That does sound like a good solution to me. We should stop accepting 
connections and log it to the log as well. We might also want to update 
the user docs and tell users to monitor the FD count as part of their 
monitoring regime. Is there a way to register for notifications on those 
via JMX? We might want to add this to our own JMX/4letterwords to 
simplify monitoring of this critical resource for users.

Travis, would you mind creating a JIRA for this? Thanks!


On 04/29/2010 10:09 AM, Travis Crawford wrote:
> On Thu, Apr 29, 2010 at 9:49 AM, Patrick Hunt<phunt@apache.org>  wrote:
>> Is there any good (simple/fast/bulletproof) way to monitor the FD use inside
>> the jvm? If so we could stop accepting new client connections once we get
>> close to the os imposed limit... The test would have to be a bulletproof one
>> though - we wouldn't want to end up in some worse situation (where we refuse
>> connection because we mistakenly believe that the limit has been reached).
>> Might be good to open a JIRA for this and add some tests. In particular we
>> should verify the server handles this as gracefully as it can when the limit
>> has been reached.
> Poking around with jconsole I found two stats that already measure FDs:
> - java.lang.OperatingSystem.MaxFileDescriptorCount
> - java.lang.OperatingSystem.OpenFileDescriptorCount
> They're described (rather tersely) at:
> http://java.sun.com/javase/6/docs/jre/api/management/extension/com/sun/management/UnixOperatingSystemMXBean.html
> So it sounds like the feature request would be stop accepting new
> client connections if OpenFileDescriptorCount>  95% of
> MaxFileDescriptorCount? Only start accepting new requests when
> OpenFileDescriptorCount<  90% of MaxFileDescriptorCount. Basically the
> high/low watermark thing.
> Thoughts?
> --travis
>> Patrick
>> On 04/29/2010 09:34 AM, Mahadev Konar wrote:
>>> Hi Travis,
>>>   How many clients did you have connected to this server? Usually the
>>> default
>>> is 8K file descriptors. Did you have clients more than that?
>>> Also, if clients fail to attach to a server, they will run off to another
>>> server. We do not do any blacklisting because we expect the server to heal
>>> and if it does not, it mostly shuts itself down in most of the cases.
>>> Thanks
>>> mahadev
>>> On 4/29/10 12:08 AM, "Travis Crawford"<traviscrawford@gmail.com>    wrote:
>>>> Hey zookeeper gurus -
>>>> We recently had a zookeeper outage when one ZK server was started with
>>>> a low limit after upgrading to 3.3.0. Several days later the outage
>>>> occurred when that node reached its file descriptor limit and clients
>>>> started having major issues.
>>>> Are there any circumstances when a ZK server will get blacklisted from
>>>> the ensemble? Something similar to how tasktrackers are blacklisted
>>>> when too many tasks fail.
>>>> Thanks!
>>>> Travis

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