Yi Liu created HDFS-8912:
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Summary: Implement ShrinkableHashMap extends java HashMap and use
properly
Key: HDFS-8912
URL: https://issues.apache.org/jira/browse/HDFS-8912
Project: Hadoop HDFS
Issue Type: Sub-task
Reporter: Yi Liu
Assignee: Yi Liu
Currently {{LightWeightHashSet}} and {{LightWeightLinkedSet}} are used in hdfs,
there are two advantages compared to java HashSet: one is the entry requires
fewer memory, another is it's shrinkable. In real cluster, hdfs is a long
running service, and {{set}} may become very large at some time and may become
small after that, so shrinking the {{set}} when size hits the shrink threshold
is necessary, it can improve the NN memory.
Same situation for {{map}}, some HashMap used in BlockManager (e.g., the
hashmap in CorruptReplicasMap), it's better to be shrinkable.
I think it's worth to implement ShrinkableHashMap extends the java HashMap,
for quick glance, seems few code is needed.
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