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https://issues.apache.org/jira/browse/YARN-3636?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14540962#comment-14540962
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Hadoop QA commented on YARN-3636:
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| (/) *{color:green}+1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:blue}0{color} | pre-patch |  14m 44s | Pre-patch trunk compilation is 
healthy. |
| {color:green}+1{color} | @author |   0m  0s | The patch does not contain any 
@author tags. |
| {color:green}+1{color} | tests included |   0m  0s | The patch appears to 
include 1 new or modified test files. |
| {color:green}+1{color} | javac |   7m 35s | There were no new javac warning 
messages. |
| {color:green}+1{color} | javadoc |   9m 35s | There were no new javadoc 
warning messages. |
| {color:green}+1{color} | release audit |   0m 22s | The applied patch does 
not increase the total number of release audit warnings. |
| {color:green}+1{color} | checkstyle |   1m  4s | There were no new checkstyle 
issues. |
| {color:green}+1{color} | whitespace |   0m  0s | The patch has no lines that 
end in whitespace. |
| {color:green}+1{color} | install |   1m 33s | mvn install still works. |
| {color:green}+1{color} | eclipse:eclipse |   0m 33s | The patch built with 
eclipse:eclipse. |
| {color:green}+1{color} | findbugs |   1m 39s | The patch does not introduce 
any new Findbugs (version 2.0.3) warnings. |
| {color:green}+1{color} | common tests |  23m 13s | Tests passed in 
hadoop-common. |
| | |  60m 21s | |
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|| Subsystem || Report/Notes ||
| Patch URL | 
http://issues.apache.org/jira/secure/attachment/12731224/0001-Abstraction-for-local-disk-path-allocation.patch
 |
| Optional Tests | javadoc javac unit findbugs checkstyle |
| git revision | trunk / f24452d |
| hadoop-common test log | 
https://builds.apache.org/job/PreCommit-YARN-Build/7904/artifact/patchprocess/testrun_hadoop-common.txt
 |
| Test Results | 
https://builds.apache.org/job/PreCommit-YARN-Build/7904/testReport/ |
| Java | 1.7.0_55 |
| uname | Linux asf902.gq1.ygridcore.net 3.13.0-36-lowlatency #63-Ubuntu SMP 
PREEMPT Wed Sep 3 21:56:12 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux |
| Console output | 
https://builds.apache.org/job/PreCommit-YARN-Build/7904/console |


This message was automatically generated.

> Abstraction for LocalDirAllocator
> ---------------------------------
>
>                 Key: YARN-3636
>                 URL: https://issues.apache.org/jira/browse/YARN-3636
>             Project: Hadoop YARN
>          Issue Type: New Feature
>    Affects Versions: 2.5.2
>            Reporter: Kannan Rajah
>              Labels: BB2015-05-TBR
>         Attachments: 0001-Abstraction-for-local-disk-path-allocation.patch
>
>
> There are 2 abstractions used to write data to local disk.
> LocalDirAllocator: Allocate paths from a set of configured local directories.
> LocalFileSystem/RawLocalFileSystem: Read/write using java.io.* and java.nio.*
> In the current implementation, local disk is managed by guest OS and not 
> HDFS. The proposal is to provide a new abstraction that encapsulates the 
> above 2 abstractions and hides who manages the local disks. This enables us 
> to provide an alternate implementation where a DFS can manage the local disks 
> and it can be accessed using HDFS APIs. This means the DFS maintains a 
> namespace for node local directories and can create paths that are guaranteed 
> to be present on a specific node.
> Here is an example use case for Shuffle: When a mapper writes intermediate 
> data using this new implementation, it will continue write to local disk. 
> When a reducer needs to access data from a remote node, it can use HDFS APIs 
> with a path that points to that node’s local namespace instead of having to 
> use HTTP server to transfer the data across nodes.
> New Abstractions
> 1. LocalDiskPathAllocator
> Interface to get file/directory paths from the local disk namespace.
> This contains all the APIs that are currently supported by LocalDirAllocator. 
> So we just need to change LocalDirAllocator to implement this new interface.
> 2. LocalDiskUtil
> Helper class to get a handle to LocalDiskPathAllocator and the FileSystem
> that is used to manage those paths.
> By default, it will return LocalDirAllocator and LocalFileSystem.
> A supporting DFS can return DFSLocalDirAllocator and an instance of DFS.
> 3. DFSLocalDirAllocator
> This is a generic implementation. An allocator is created for a specific 
> node. It uses Configuration object to get user configured base directory and 
> appends the node hostname to it. Hence the returned paths are within the node 
> local namespace.



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