[HDFS-1446] Refactor the start-time Directory Tree and Replicas Map constructors to share data and run volume-parallel

• Type: Sub-task
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 0.20.2
• Component/s: datanode
• Tags: datanode startup, volume parallel
• Assignee: Matthew Foley
• Reporter: Matthew Foley
• Created: 07/Oct/10 22:39
• Updated: 13/Jan/11 02:22

Description

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.