GitHub user liancheng opened a pull request:
https://github.com/apache/spark/pull/12527
[SPARK-14369][SQL] Locality support for FileScanRDD
(This PR is a rebased version of PR #12153.)
## What changes were proposed in this pull request?
This PR adds preliminary locality support for `FileFormat` data sources by
overriding `FileScanRDD.preferredLocations()`. The strategy can be divided into
two parts:
1. Block location lookup
Unlike `HadoopRDD` or `NewHadoopRDD`, `FileScanRDD` doesn't have access
to the underlying `InputFormat` or `InputSplit`, and thus can't rely on
`InputSplit.getLocations()` to gather locality information. Instead, this PR
queries block locations using `FileSystem.getBlockLocations()` after listing
all `FileStatus`es in `HDFSFileCatalog` and convert all `FileStatus`es into
`LocatedFileStatus`es.
Note that although S3/S3A/S3N file systems don't provide valid locality
information, their `getLocatedStatus()` implementations don't actually issue
remote calls either. So there's no need to special case these file systems.
2. Selecting preferred locations
For each `FilePartition`, we pick up top 3 locations that containing
the most data to be retrieved. This isn't necessarily the best algorithm out
there. Further improvements may be brought up in follow-up PRs.
## How was this patch tested?
Tested by overriding default `FileSystem` implementation for `file:///`
with a mocked one, which returns mocked block locations.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/liancheng/spark spark-14369-locality-rebased
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/12527.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #12527
----
commit 0358e33c1a796b7875f932c4d4aee28db505f696
Author: Cheng Lian <[email protected]>
Date: 2016-04-20T13:25:51Z
Rebased PR #12153
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