Jing Zhao created HDFS-5714:
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             Summary: Use byte array to represent UnderConstruction feature and 
Snapshot feature for INodeFile
                 Key: HDFS-5714
                 URL: https://issues.apache.org/jira/browse/HDFS-5714
             Project: Hadoop HDFS
          Issue Type: Sub-task
            Reporter: Jing Zhao
            Assignee: Jing Zhao


Currently we define specific classes to represent different INode features, 
such as FileUnderConstructionFeature and FileWithSnapshotFeature. While 
recording these feature information in memory, the internal information and 
object references can still cost a lot of memory. For example, for 
FileWithSnapshotFeature, not considering the INode's local name, the whole 
FileDiff list (with size n) can cost around 120n bytes.

In order to decrease the memory usage, we plan to use byte array to record the 
UnderConstruction feature and Snapshot feature for INodeFile. Specifically, if 
we use protobuf's encoding, the memory usage for a FileWithSnapshotFeature can 
be less than 56n bytes.



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