[HDFS-202] Add a bulk FIleSystem.getFileBlockLocations

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.22.0
• Component/s: hdfs-client, namenode
• Hadoop Flags: Incompatible change, Reviewed
• Assignee: Hairong Kuang
• Reporter: Arun Murthy
• Created: 08/May/09 17:21
• Updated: 12/Dec/11 06:20
• Resolved: 11/Aug/10 20:46

Description

Currently map-reduce applications (specifically file-based input-formats) use FileSystem.getFileBlockLocations to compute splits. However they are forced to call it once per file.
The downsides are multiple:

1. Even with a few thousand files to process the number of RPCs quickly starts getting noticeable
2. The current implementation of getFileBlockLocations is too slow since each call results in 'search' in the namesystem. Assuming a few thousand input files it results in that many RPCs and 'searches'.

It would be nice to have a FileSystem.getFileBlockLocations which can take in a directory, and return the block-locations for all files in that directory. We could eliminate both the per-file RPC and also the 'search' by a 'scan'.

When I tested this for terasort, a moderate job with 8000 input files the runtime halved from the current 8s to 4s. Clearly this is much more important for latency-sensitive applications...

Issue Links

• blocks: MAPREDUCE-1981 Improve getSplits performance by using listLocatedStatus
• relates to: HADOOP-6870 Add FileSystem#listLocatedStatus to list a directory's content together with each file's block locations