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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4539) Streaming Edits to a Standby Name-Node.
Date Fri, 13 Mar 2009 17:15:56 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4539?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12681830#action_12681830

Suresh Srinivas commented on HADOOP-4539:

1. I think it might be a good idea to abstract the active/backup/checkpointer as states of
Namenode. This helps in transition of states back and forth. In current design an active node
cannot become backup. This can be done in a separate jira.

Coding related:

bq. 6.1. I think that ServerCommand actions (static ints) should belong to the commands that
use them. I plan to file an issue to move DatanodeCommand actions into the respective commands.
I am not clear on this. Since ACT_SHUTDOWN is part of protocol itself, it should be in NamenodeProtocol.java?

bq. 8.3. dfs.backup.address and dfs.backup.http.address define the addresses which the backup
node starts on its rpc and http servers. You do not need to change the configuration when
the node transitions from backup to active.
Example. If you start DataNode on port 0, which means on any free port, you do not change
the config file after startup, right? Same with backup/active nodes.

My example is more like: Say you configure address X as active and address Y as backup during
install time. Now for some reason you want to start active node on Y. At this time the addresses
that Y tries to bind to address X. Similarly starting backup on X will result in X trying
to bind to address Y. So irrespective of local address, the services start on configured addresses.
I am not sure this can be solved until we have node management as a part of HA that can assign
roles to the nodes. Nodes always bind to their local address and start or transition to the
role they are assigned.

> 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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