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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1070) Speedup NameNode image loading and saving by storing local file names
Date Wed, 01 Dec 2010 23:12:16 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12965917#action_12965917
] 

Hairong Kuang commented on HDFS-1070:
-------------------------------------

I did some experiments with one of our internal image.
1. the image is not compressed
|| ||Full Path Image||Local Name Image||
|Image Size|14.2G|7.3G|
|Loading Time(s)|443|309|
|Saving Time(s)|224|126|
2. the image is compressing using LZOP codec
|| ||Full Path Image||Local Name Image||
|Image Size|3.0G|2.8G|
|Loading Time(s)|565|467|
|Saving Time(s)|251|231|

We can see that this feature could cut the image size by half  and cut the loading/saving
time significantly if the image is not compressed. If the image is compressed, the benefit
is not as significant but still it improves loading and saving time.

> 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
>             Fix For: 0.22.0
>
>         Attachments: trunkLocalNameImage.patch, trunkLocalNameImage1.patch, trunkLocalNameImage3.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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