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From "Lei Xia (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HELIX-527) Mitigate zookeeper watch leak
Date Wed, 31 Aug 2016 17:44:21 GMT

    [ https://issues.apache.org/jira/browse/HELIX-527?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15452861#comment-15452861
] 

Lei Xia commented on HELIX-527:
-------------------------------

We may need to reevaluate this issue and figure out the solution.  Assigned to me, and I will
spend some time on this issue.

> Mitigate zookeeper watch leak
> -----------------------------
>
>                 Key: HELIX-527
>                 URL: https://issues.apache.org/jira/browse/HELIX-527
>             Project: Apache Helix
>          Issue Type: Bug
>            Reporter: Zhen Zhang
>
> 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



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