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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-6678) Propose some changes to FileContext
Date Mon, 05 Apr 2010 22:00:27 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-6678?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12853558#action_12853558
] 

Hairong Kuang commented on HADOOP-6678:
---------------------------------------

> I cold do part 2 in lieu of HADOOP-6585 (Add FileStatus#isDirectory and isFile) and HDFS-995,
MR-1535.
Eli, thanks for volunteering to do part 2. Your help would be great!

> Propose some changes to FileContext
> -----------------------------------
>
>                 Key: HADOOP-6678
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6678
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs
>            Reporter: Hairong Kuang
>             Fix For: 0.21.0, 0.22.0
>
>
> # Add a method  Iterator<FileStatus> listStatus(Path), which allows HDFS client
not to have the whole listing in the memory, benefit more from the iterative listing added
in HDFS-985. Move the current FileStatus[] listStatus(Path) to be a utility method.
> # Remove methods isFile(Path), isDirectory(Path), and exists.
> All these methods are implemented by calling getFileStatus(Path).But most users are not
aware of this. They would write code as below: 
> {code}
>   FileContext fc = ..;
>   if (fc.exists(path)) {
>     if (fc.isFile(path)) {
>      ...
>     } else {
>     ...
>     }
>   }
> {code}
> The above code adds unnecessary getFileInfo RPC to NameNode. In our production clusters,
we often see that the number of getFileStatus calls is multiple times of the open calls. If
we remove isFile, isDirectory, and exists from FileContext, users have to explicitly call
getFileStatus first, it is more likely that they will write more efficient code as follow:
> {code}
>   FileContext fc = ...;
>   FileStatus fstatus = fc.getFileStatus(path);
>   if (fstatus.isFile() {
>     ...
>   } else {
>     ...
>   }
> {code}

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