Travis Crawford commented on ZOOKEEPER-856:

Thanks for the suggestions! I'm trying out the following options:


I still think the connection imbalance issue is worth addressing though. Even 
with properly tuned ZK servers they can become overloaded as older processes 
acquire connections to the point of becoming overloaded.

> 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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