More CPU efficient data structure for
under-replicated/over-replicated/invalidate blocks
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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
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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