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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4539) Streaming Edits to a Standby Name-Node.
Date Fri, 13 Mar 2009 17:28:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12681833#action_12681833

Tsz Wo (Nicholas), SZE commented on HADOOP-4539:

> In general I don't also see a reason why NameNode.myMetrics should be a static member.

Static variables sometimes are misused as global variables.  This is one example.  Another
one is FSNamesystem.fsNamesystemObject (see HADOOP-2413).

BTW, could you not using the deprecated API FSNamesystem.getFSNamesystem() in BackupStorage?
+  private FSNamesystem getFSNamesystem() {
+    // HADOOP-5119 should get rid of this.
+    return FSNamesystem.getFSNamesystem();
+  }
I suggest passing a FSNamesystem object in the constructor BackupStorage().  Then, pass the
FSNamesystem object created in BackupNode.loadNamesystem(..), which is the only place creating
a BackupStorage.

> Streaming Edits to a Standby Name-Node.
> ---------------------------------------
>                 Key: HADOOP-4539
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4539
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: Konstantin Shvachko
>            Assignee: Konstantin Shvachko
>             Fix For: 0.21.0
>         Attachments: BackupNode.patch, BackupNode.patch, BackupNode.patch, BackupNode.patch,
image001.gif, StreamEditsToBN.pdf, StreamEditsToSNN.htm
> Currently Secondary name-node acts as mere checkpointer.
> Secondary name-node should be transformed into a standby name-node (SNN). 
> The long term goal is to make it a warm standby. 
> The purpose of this issue is to provide real time streaming of edits to SNN so that it
contained the up-to-date namespace state.

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