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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1435) Provide an option to store fsimage compressed
Date Fri, 15 Oct 2010 00:51:36 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12921193#action_12921193
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dhruba borthakur commented on HDFS-1435:
----------------------------------------

I looked at the code, looks good. Have two comments:

1. I would prefer to have the compression start after the header record. For example, the
imgVersion, numFiles, genStamp, defaultReplication, etc not be compressed. This allows easier
debugging, ability to dump the header of a file to find out its contents (via od -x), etc.

2. The new image version is 25. but the code refers to it as -19

{code}
      if (imgVersion <= -19) {  // -19: 1st version providing compression option
        isCompressed = in.readBoolean();
        if (isCompressed) {
          String codecClassName = Text.readString(in);
{code}

> 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
>
>         Attachments: checkpoint-limitandcompress.patch, trunkImageCompress.patch, trunkImageCompress1.patch
>
>
> 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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