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Date: Mon, 5 Apr 2010 18:01:28 +0000 (UTC)
From: "Todd Lipcon (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-6678) Propose some changes to FileContext
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    [ https://issues.apache.org/jira/browse/HADOOP-6678?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12853468#action_12853468 ] 

Todd Lipcon commented on HADOOP-6678:
-------------------------------------

OK, sounds good. Thanks for the info, Hairong.

> 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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