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https://issues.apache.org/jira/browse/HDFS-202?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12752748#action_12752748
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Sanjay Radia commented on HDFS-202:
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Is the optimization for sending only partial block reports really necessary?
Most files have very few blocks ...
Also arun's point of doing an extra call for doing the getFileStatus() is valid.
Why not create a class called DetailedFileStatus which contains both the file
status and block locations:
DetailedFileStatus[] = getBlockLocations(Path[] paths); // 1:1 mapping between
the two arrays as Doug suggested.
We can add the range one later if we really need that optimization.
> Add a bulk FIleSystem.getFileBlockLocations
> -------------------------------------------
>
> Key: HDFS-202
> URL: https://issues.apache.org/jira/browse/HDFS-202
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Arun C Murthy
> Assignee: Jakob Homan
>
> 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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