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https://issues.apache.org/jira/browse/HADOOP-5795?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12708433#action_12708433
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dhruba borthakur commented on HADOOP-5795:
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Ok, so from what I can understand, here is the proposal:
Map<FileStatus, BlockLocation[]> listBlockLocations(Path[] inputPaths);
The "inputPaths" can be a set of files and/or directories. If one of the
inputPaths is a directory, then all items inside that directory (only one
level, not recursive) are listed and their block locations are returned by this
call. if one of the inputPaths is a file, then its block locations are returned
by this call. The FileStatus returned by this call should have the absolulte
path of the object being returned.
> Add a bulk FIleSystem.getFileBlockLocations
> -------------------------------------------
>
> 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
> Assignee: Jakob Homan
> 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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