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From Bram Biesbrouck...@beligum.com>
Subject Re: Found weird issue with HttpFS and WebHdfsFileSystem
Date Fri, 17 Apr 2015 12:26:35 GMT
Hi Chris,

Thanks for this reply. I thought something funny was happening.

The childNum field is actually very useful (eg for (not) rendering a
expansion marker next to a folder in a GUI when it has children), so it's a
pity the info is there, but get's "eaten up" by the general interface, only
to be re-calculated later on.
It would be nice to have the info as an optional field in the FileStatus
class (initialized to -1 like it is right now), so we can use it if it's
there or just ignore it when not initialized. While I'm
ranting, HdfsFileStatus should override from FileStatus because it's 95%
the same code anyway.

If I read your reply correctly, I assume the fields will be deleted from
the webhdfs JSON responses as well in the future?

Thanks again for the extensive reply, very useful and appreciated.

cheers,

b.



On Fri, Apr 17, 2015 at 12:59 AM, Chris Nauroth <cnauroth@hortonworks.com>
wrote:

>  Hello Bram,
>
>  There are a few Apache jiras with background discussion of the
> introduction of these fields in WebHDFS.
>
>  https://issues.apache.org/jira/browse/HDFS-4502
>
>  https://issues.apache.org/jira/browse/HDFS-4772
>
>  https://issues.apache.org/jira/browse/HDFS-4969
>
>  The new fields could not be supported in HTTPFS (only WebHDFS), and they
> were not intended to be guaranteed in the public REST API.  Unfortunately,
> the fields were added to the documentation mistakenly in Apache Hadoop
> 2.5.0.
>
>  https://issues.apache.org/jira/browse/HDFS-6153
>
>  We're going to revert that documentation change in Apache Hadoop 2.8.0.
> I suggest that your application does not rely on these fields, or at least
> includes fallback logic to keep working as best as it can if the fields are
> not present.  Another way to determine the number of children would be to
> make a subsequent LISTSTATUS call on the child path.
>
>  I apologize if this caused any inconvenience, and I hope the information
> helps.
>
>   Chris Nauroth
> Hortonworks
> http://hortonworks.com/
>
>
>   From: Bram Biesbrouck <b@beligum.com>
> Reply-To: "user@hadoop.apache.org" <user@hadoop.apache.org>
> Date: Thursday, April 16, 2015 at 7:58 AM
> To: "user@hadoop.apache.org" <user@hadoop.apache.org>
> Subject: Found weird issue with HttpFS and WebHdfsFileSystem
>
>   Hi all,
>
>  I'm experiencing something strange while developing against the HttpFS
> front-end webapp on Hadoop 2.6.0.
>
>  I'm currently digging into WebHdfsFileSystem and HttpFS to understand it
> better and understand how the rest api works. I've setup a local single
> node Hadoop instance, which I can query successfully with eg.
> http://localhost:50070/webhdfs/v1/?op=LISTSTATUS
> Returning eg. this FileStatus object:
>
>  {
> accessTime: 0,
> blockSize: 0,
> childrenNum: 0,
> fileId: 16386,
> group: "supergroup",
> length: 0,
> modificationTime: 1417964248854,
> owner: "hadoop",
> pathSuffix: "user",
> permission: "755",
> replication: 0,
> storagePolicy: 0,
> type: "DIRECTORY"
> }
>
>  Now, when I start HttpFS and ask for the same data over it's interface (
> http://localhost:14000/webhdfs/v1/?op=LISTSTATUS), I get a different
> reply. Especially, the childrenNum and fileId fields are missing, compared
> to the first result (same file or directory):
>
>  {
> pathSuffix: "user",
> type: "DIRECTORY",
> length: 0,
> owner: "hadoop",
> group: "supergroup",
> permission: "755",
> accessTime: 0,
> modificationTime: 1417964248854,
> blockSize: 0,
> replication: 0
> }
>
>  Since I need the childrenNum property, I started digging into the code
> to see where it's "lost" and found that WebHdfsFileSystem performs a
> makeQualified() step (around line 1287 in WebHdfsFileSystem.java), just
> before the list of filestatuses is returned. Basically, it converts
> HdfsFileStatus objects into FileStatus objects, effectively chopping off
> those two properties.
>
>  The sources for HdfsFileStatus clearly state that it's an "Interface
> that represents the over the wire information for a file.", so I wonder why
> this happens, since the HdfsFileStatus contains all the right properties,
> according to the docs at
> http://hadoop.apache.org/docs/r2.6.0/hadoop-project-dist/hadoop-hdfs/WebHDFS.html#List_a_Directory
>
>  It feels like the FileStatus class hasn't been updated to match the
> HdfsFileStatus class, but since they don't share any interfaces or
> superclasses I get the feeling it's intentional, but I just can't find or
> figure out why.
>
>  Can somebody help or shed some light?
>
>  thanks,
>
>  b.
> --
>
>  Bram Biesbrouck - 0486/118280 - www.beligum.com -  the republic of
> reinvention
>
>


-- 

 Bram Biesbrouck - 0486/118280 - www.beligum.com -  the republic of
reinvention

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