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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4539) Streaming Edits to a Standby Name-Node.
Date Thu, 19 Feb 2009 22:06:02 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12675151#action_12675151
] 

Konstantin Shvachko commented on HADOOP-4539:
---------------------------------------------

(Dhruba-1) Current implementation supports only one Backup node. It will just not let the
other register once one is already registered. This is the implementation restriction only.
We can extend it by providing a Collection of registered backup nodes on the active node.
Something to work on in the future. You can have multiple checkpointers though as long as
there are no any backups.
(Dhruba-2) Bookkeeper integration is a separate issue but related. Separate because BK provides
only the journalling functionality. You cannot keep an up-to-date namespace in BK, and even
if you do it is not useful for the name-node. Separate because fast journalling is important
and that is what BK provides, while backup nodes are still bounded by the local disk speed.
Related since both should use the same abstractions for journalling - abstract edit streams
under the common journalling framework.

> 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
>         Attachments: BackupNode.patch, image001.gif, 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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