Add a bulk FIleSystem.getFileBlockLocations
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Key: HADOOP-5795
URL: https://issues.apache.org/jira/browse/HADOOP-5795
Project: Hadoop Core
Issue Type: New Feature
Components: dfs
Affects Versions: 0.20.0
Reporter: Arun C Murthy
Fix For: 0.21.0
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:
# Even with a few thousand files to process the number of RPCs quickly
starts getting noticeable
# 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...
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