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From "Karthik Kambatla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5268) Improve history server startup performance
Date Wed, 29 May 2013 16:36:21 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5268?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13669406#comment-13669406
] 

Karthik Kambatla commented on MAPREDUCE-5268:
---------------------------------------------

bq. I think we'd have to use a weighted cache with the weight being an increasing sequence
number so it removes entries based on cache size but in insertion order rather than LRU.

Also, we will have to set the concurrency level to 1 to ensure the weighted cache follows
the order.

bq. I'm OK with the current approach with one suggestion: I'd prefer the size/collection pair
implementation detail abstracted into a local utility class.

Makes total sense. Will do.
                
> Improve history server startup performance
> ------------------------------------------
>
>                 Key: MAPREDUCE-5268
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5268
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: jobhistoryserver
>    Affects Versions: 0.23.7, 2.0.4-alpha
>            Reporter: Jason Lowe
>            Assignee: Karthik Kambatla
>         Attachments: mr-5268.patch, mr-5268-prelim.patch
>
>
> The history server can easily take many minutes to startup when there are a significant
number of jobs to scan in the done directory.  However the scanning of files is not the bottleneck,
rather it's the heavy use of ConcurrentSkipListMap.size in HistoryFileManager.  
> ConcurrentSkipListMap.size is a very expensive operation, especially on maps with many
entries, as it has to scan every entry to compute the size.  We should avoid calling this
method or at least minimize its use.

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