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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2026) 1073: 2NN needs to handle case of reformatted NN better
Date Tue, 21 Jun 2011 22:37:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2026?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13052908#comment-13052908
] 

Todd Lipcon commented on HDFS-2026:
-----------------------------------

bq. Can we remove Checkpointer#uploadCheckpoint commented out? 
Added TODO -- the CN/BN will be addressed separately

bq. testReformatNNBetweenCheckpoints method comment is missing a period
fixed

bq. The new call to sd.read in SecondaryNameNode#recoverCreate could use a comment
added:
{code}
          case NORMAL:
            // Read the VERSION file. This verifies that:
            // (a) the VERSION file for each of the directories is the same,
            // and (b) when we connect to a NN, we can verify that the remote
            // node matches the same namespace that we ran on previously.
            sd.read();
            break;
{code}

bq. As an aside, readVersionFile would be a better name for that method
I agree, but we should do that separately -- this function gets used throughout all of HDFS
(eg also on the DN side)

bq. Not you change would be good to add a comment to uploadImageFromStorage indicating it
doesn't actually post an image but the 2NN posts to the NN asking it to get an image
Added the following javadoc:
{code}
  /**
   * Requests that the NameNode download an image from this node.
   *
   * @param fsName the http address for the remote NN
   * @param imageListenAddress the host/port where the local node is running an
   *                           HTTPServer hosting GetImageServlet
   * @param storage the storage directory to transfer the image from
   * @param txid the transaction ID of the image to be uploaded
   */
{code}
and this comment:
{code}
    // this doesn't directly upload an image, but rather asks the NN
    // to connect back to the 2NN to download the specified image.
    TransferFsImage.getFileClient(fsName, fileid, null, false);
...
{code}

> 1073: 2NN needs to handle case of reformatted NN better
> -------------------------------------------------------
>
>                 Key: HDFS-2026
>                 URL: https://issues.apache.org/jira/browse/HDFS-2026
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>    Affects Versions: Edit log branch (HDFS-1073)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Critical
>             Fix For: Edit log branch (HDFS-1073)
>
>         Attachments: hdfs-2026.txt
>
>
> Currently in the 1073 branch, the following steps ends up with a very confused 2NN:
> - format NN, run NN
> - start 2NN, perform some checkpoints
> - reformat NN, start NN on new namespace
> - restart same 2NN
> The 2NN currently saves the new VERSION info into its local storage directory but doesn't
clear out the old checkpoint or edits files. This is obviously wrong and might lead to a corrupt
checkpoint getting uploaded. 
> If the 2NN has storage directories with VERSION info, and connects to an NN with different
VERSION info, there are two alternatives:
> a) refuse to perform any checkpoints until the operator issues a "secondarynamenode -format"
command (this is similar to how the backupnode/checkpointnode works)
> b) clear the current contents of the storage directory and save the new NN's VERSION
info.

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