Patrick Hunt commented on ZOOKEEPER-856:

Well it could be that increased connection count correlates to increased 
activity, including longer gc pauses as a result.

I believe incremental mode is what you're looking for (just one reference):

"The incremental mode is meant to lessen the impact of long concurrent phases 
by periodically stopping the concurrent phase to yield back the processor to 
the application."

I've found this tool to be an excellent way to visualize GC activity: 

Also, have you verified that you are not using a large % of the heap? Perhaps 
you could include some JVM stats (heap utilization say) in your monitoring 

> 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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