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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1070) Speedup NameNode image loading and saving by storing local file names
Date Tue, 05 Apr 2011 00:31:05 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13015701#comment-13015701
] 

Tsz Wo (Nicholas), SZE commented on HDFS-1070:
----------------------------------------------

Here is an orthogonal idea for reducing image size:

In NameNode, we have internal maps for usernames, groups to serial numbers (see {{SerialNumberManager}})
in order to save memory in the NameNode.  How about we do the same for {{FSImage}}?  I.e.
write the maps in the beginning of {{FSImage}} and then use the serial numbers in the {{INode}}
entries.

Suppose the saving is 10 bytes per name, that is 20 bytes per {{INode}}.  Then, it is about
1.1 GB for a namespace with 60 million files/directories.

> Speedup NameNode image loading and saving by storing local file names
> ---------------------------------------------------------------------
>
>                 Key: HDFS-1070
>                 URL: https://issues.apache.org/jira/browse/HDFS-1070
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>         Attachments: trunkLocalNameImage.patch, trunkLocalNameImage1.patch, trunkLocalNameImage3.patch,
trunkLocalNameImage4.patch, trunkLocalNameImage5.patch
>
>
> Currently each inode stores its full path in the fsimage. I'd propose to store the local
name instead. In order for each inode to identify its parent, all inodes in a directory tree
are stored in the image in in-order. This proposal also requires each directory stores the
number of its children in image.
> This proposal would bring a few benefits as pointed below and therefore speedup the image
loading and saving.
> # Remove the overhead of converting java-UTF8 encoded local name to string-represented
full path then to UTF8 encoded full path when saving to an image and vice versa when loading
the image.
> # Remove the overhead of traversing the full path when inserting the inode to its parent
inode.
> # Reduce the number of temporary java objects during the process of image loading or
saving and  therefore reduce the GC overhead.
> # Reduce the size of an image.

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