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https://issues.apache.org/jira/browse/HADOOP-4539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12675151#action_12675151
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Konstantin Shvachko commented on HADOOP-4539:
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(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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