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https://issues.apache.org/jira/browse/STORM-4052?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Richard Zowalla closed STORM-4052.
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Resolution: Fixed
> Simplify/Remove double delete/lookup in heartbeat cleanup code
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>
> Key: STORM-4052
> URL: https://issues.apache.org/jira/browse/STORM-4052
> Project: Apache Storm
> Issue Type: Bug
> Affects Versions: 2.6.1, 2.6.2
> Reporter: Richard Zowalla
> Priority: Major
> Fix For: 2.6.3
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> This changes slightly simplifies the heartbeat cleanup code so it no longer
> tries to delete the heartbeat files twice. It also removes an unneeded
> directory listing (and possible race) by truncating the versions list and
> using it for removal instead of for keeping.
> Removing the double delete attempt is important because it removes a lookup
> for now non-existent files. Looking up non existent files, especially highly
> unique (like timestamped) ones can adversely affect many operating systems as
> these lookups are cached as negative dentries.
> [https://lwn.net/Articles/814535/]
> When cleanup runs, it iterates over the heartbeat directory that contains a
> token and version file for each heartbeat. It calls deleteVersion for each
> file in the directory which attempts to delete both files associated with the
> heartbeat. As deleteVersion already deletes both when it first iterates over
> the token file, the iteration for the version file has nothing to do.
> Before removing, the deleteVersion code checks for the existence of these now
> non existent files. On linux (and other OSs) a lookup for a non-existent path
> will create a negative dentry in the operating system's cache. On some
> configurations this cache can grow effectively unbounded leading to
> performance issues. On newer systems this cache is better managed, but this
> will still dilute an otherwise useful OS cache with useless entries.
>
> Copied from [https://github.com/apache/storm/pull/3635] (Author: sammac)
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