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https://issues.apache.org/jira/browse/HDFS-2476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13164814#comment-13164814
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Eli Collins commented on HDFS-2476:
-----------------------------------
Why do we need to use a LightWeightLinkedSet for excessReplicateMap? It doesn't
seem like we need to preserve order traversal for excess replicas and this
would save the overhead of allocating a list.
> 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
> Fix For: 0.24.0
>
> Attachments: hashStructures.patch, hashStructures.patch-2,
> hashStructures.patch-3, hashStructures.patch-4, hashStructures.patch-5,
> hashStructures.patch-6, hashStructures.patch-7, hashStructures.patch-8,
> hashStructures.patch-9
>
>
> 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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