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<ph...@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:


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.




On 04/29/2010 09:34 AM, Mahadev Konar wrote:

Hi Travis,

  How many clients did you have connected to this server? Usually the
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.


On 4/29/10 12:08 AM, "Travis Crawford"<traviscrawf...@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.


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