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Date: Sat, 22 Oct 2011 08:12:33 +0000 (UTC)
From: "Tomasz Nykiel (Commented) (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-2476) More CPU efficient data structure
 for under-replicated/over-replicated/invalidate blocks
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    [ https://issues.apache.org/jira/browse/HDFS-2476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13133309#comment-13133309 ] 

Tomasz Nykiel commented on HDFS-2476:
-------------------------------------

Todd, thanks for your comments. I applied your suggestions, and fixed some bugs. The code is essentially what we are using in production. Although, our branch is quite off the trunk, so it's not really one-to-one mapping.

There is still some JUnit tests failing, although they seem to be older. 
The rest of them should pass with the latest patch. 
                
> 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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