Travis Crawford commented on ZOOKEEPER-856:

@patrick - We're using these settings, which I believe are based on what's 
recommended in the troubleshooting guide.


Looking at the logs I do see lots of GC activity. For example:

Total time for which application threads were stopped: 0.5599050 seconds
Application time: 0.0056590 seconds

I only see this on the hosts that became unresponsive after acquiring lots of 

Any suggestions for the GC flags? If there's something better I can experiment, 
and update the wiki if we discover something interesting.


> Connection imbalance leads to overloaded ZK instances
> -----------------------------------------------------
>                 Key: ZOOKEEPER-856
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-856
>             Project: Zookeeper
>          Issue Type: Bug
>            Reporter: Travis Crawford
>             Fix For: 3.4.0
>         Attachments: zk_open_file_descriptor_count_members.gif, 
> zk_open_file_descriptor_count_total.gif
> We've experienced a number of issues lately where "ruok" requests would take 
> upwards of 10 seconds to return, and ZooKeeper instances were extremely 
> sluggish. The sluggish instance requires a restart to make it responsive 
> again.
> I believe the issue is connections are very imbalanced, leading to certain 
> instances having many thousands of connections, while other instances are 
> largely idle.
> A potential solution is periodically disconnecting/reconnecting to balance 
> connections over time; this seems fine because sessions should not be 
> affected, and therefore ephemaral nodes and watches should not be affected.

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