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From "Steve Loughran (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2476) More CPU efficient data structure for under-replicated/over-replicated/invalidate blocks
Date Mon, 24 Oct 2011 16:09:33 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13134193#comment-13134193

Steve Loughran commented on HDFS-2476:

Tomasz, I've probably just possibly made your patch hard to apply in HDFS-2485 -but that won't
impact your code at all. Can you merge your changes into trunk and resubmit?

Like I said before, hadoop-common would be the best place for the structures as the other
parts of the system can pick them up there. That will mean
 # splitting out the data structures and tests
 # packaging under hadoop common and not hdfs.
 # adding a (linked) hadoop common issue
> More CPU efficient data structure for under-replicated/over-replicated/invalidate blocks
> ----------------------------------------------------------------------------------------
>                 Key: HDFS-2476
>                 URL: https://issues.apache.org/jira/browse/HDFS-2476
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>            Reporter: Tomasz Nykiel
>            Assignee: Tomasz Nykiel
>         Attachments: hashStructures.patch, hashStructures.patch-2, hashStructures.patch-3,
hashStructures.patch-4, hashStructures.patch-5
> This patch introduces two hash data structures for storing under-replicated, over-replicated
and invalidated blocks. 
> 1. LightWeightHashSet
> 2. LightWeightLinkedSet
> Currently in all these cases we are using java.util.TreeSet which adds unnecessary overhead.
> The main bottlenecks addressed by this patch are:
> -cluster instability times, when these queues (especially under-replicated) tend to grow
quite drastically,
> -initial cluster startup, when the queues are initialized, after leaving safemode,
> -block reports,
> -explicit acks for block addition and deletion
> 1. The introduced structures are CPU-optimized.
> 2. They shrink and expand according to current capacity.
> 3. Add/contains/delete ops are performed in O(1) time (unlike current log n for TreeSet).
> 4. The sets are equipped with fast access methods for polling a number of elements (get+remove),
which are used for handling the queues.

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