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https://issues.apache.org/jira/browse/HELIX-504?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14145049#comment-14145049
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Zhen Zhang commented on HELIX-504:
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On investigating zookeeper watch leakage problem, it turns out to be a
zookeeper issue:
https://issues.apache.org/jira/browse/ZOOKEEPER-442
For zookeeper before 3.5.0, we can't remove watches that are no longer of
interests. The only way to remove a watch is to trigger it; that is, if it is a
DataWatch, we need to trigger a data change on the watching path, or if it is a
ChildWatch, we need to trigger a child change on the watching path.
Unfortunately, if we are watching a path that has been deleted, unless we
re-create the path, there is no way we can remove the watch.
Here are some of the most common scenarios where we will have dead zookeeper
watches on zookeeper server side even though we unregister all the listeners on
the zookeeper client side:
- When we drop a resource group from a cluster, we may have dead watches on
ideal-state, participant current-state, and external-view
- When we remove an instance from a cluster, we may have dead watches on
current-state, participant-config, and participant messages
- When we use property store with caches enabled by zookeeper watches, we may
have dead watches on all removed paths
Will create separate jiras to track the issue.
> Controller should avoid resetting watches on removed paths
> ----------------------------------------------------------
>
> Key: HELIX-504
> URL: https://issues.apache.org/jira/browse/HELIX-504
> Project: Apache Helix
> Issue Type: Bug
> Reporter: Kanak Biscuitwala
> Assignee: Zhen Zhang
>
> Right now, if a participant has a session change, the old current state will
> be removed, but the controller despite unregistering the listener, still
> reset the watch on the path deleted event. We should avoid resetting this
> path on delete and let the controller explicitly set watches/listeners on new
> sessions.
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