[HDFS-12589] [DISCUSS] Provided Storage BlockAlias Refactoring

• Type: Sub-task
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: hdfs
• Assignee: Unassigned
• Reporter: Ewan Higgs
• Created: 04/Oct/17 09:31
• Updated: 04/Oct/17 09:34

Description

A BlockAlias is an interface used by the Datanode to determine where to retrieve data from. It currently has a single implementation: FileRegion which contains the Block, BlockPoolID, Provided URL for the FileRegion (i.e. block); and length and offset of the FileRegion in the remote storage.

The BlockAlias currently has a single method: getBlock. This is not particularly useful since we can't ask it meaningful questions like 'how do we retrieve the data from the external storage system?'. Or 'is the version of the block in the external storage system up to data?'. Either we can do away with the BlockAlias altogether and work with FileRegion, or the BlockAlias needs to be made more robust.