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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1435) Provide an option to store fsimage compressed
Date Thu, 07 Oct 2010 22:02:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12919079#action_12919079
] 

Doug Cutting commented on HDFS-1435:
------------------------------------

Hairong, Avro's file format has little overhead.  It supports compression.  However it assumes
that a file is composed of a sequence of entries with a the same schema.  The fsimage has
various sections.  The header information could be added as Avro file metadata.  The files
and directories, datanodes and files under construction are currently written as separate
blocks.  Instead, the schema for every item might be something like a union of [File, Directory,
Symlink, DataNode, FileUnderConstruction].

> Provide an option to store fsimage compressed
> ---------------------------------------------
>
>                 Key: HDFS-1435
>                 URL: https://issues.apache.org/jira/browse/HDFS-1435
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>    Affects Versions: 0.22.0
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: 0.22.0
>
>
> Our HDFS has fsimage as big as 20G bytes. It consumes a lot of network bandwidth when
secondary NN uploads a new fsimage to primary NN.
> If we could store fsimage compressed, the problem could be greatly alleviated.
> I plan to provide a new configuration hdfs.image.compressed with a default value of false.
If it is set to be true, fsimage is stored as compressed.
> The fsimage will have a new layout with a new field "compressed" in its header, indicating
if the namespace is stored compressed or not.

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