[HDFS-dev] [jira] Created: (HDFS-1446) Refactor the start-time Directory Tree and Replicas Map constructors to share data and run volume-parallel

Refactor the start-time Directory Tree and Replicas Map constructors to share data and run volume-parallel
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Key: HDFS-1446
URL: https://issues.apache.org/jira/browse/HDFS-1446
Project: Hadoop HDFS
Issue Type: Sub-task
Components: data-node
Affects Versions: 0.20.2
Reporter: Matt Foley
Assignee: Matt Foley
Fix For: 0.22.0


Refactor the FSDir() and getVolumeMap() call chains in FSDataset, so they share data and run volume-parallel. Currently the two constructors for in-memory directory tree and replicas map run THREE full scans of the entire disk - once in FSDir(), once in recoverTempUnlinkedBlock(), and once in addToReplicasMap(). During each scan, a new File object is created for each of the 100,000 or so items in the native file system (for a 50,000-block node). This impacts GC as well as disk traffic.

This work item is one of four sub-tasks for HDFS-1443, Improve Datanode startup time.