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https://issues.apache.org/jira/browse/HDFS-839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12800226#action_12800226
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Wang Xu commented on HDFS-839:
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Hi Dhruba,
Thanks for your reply
On Thu, Jan 14, 2010 at 10:40 PM, dhruba borthakur (JIRA) <[email protected]>
wrote:
> 1. new transactions from clients are blocked when the primary namenode is
> syncing transactions to a new slave
For those modifing metadata, it is blocked.
> 2. The automatic promotion of a slave to be a master (when the original
> master dies) based on zookeper is something for the future
Yes.
> 3. The datanodes will send block reports only to the master. so when a
> failover occurs you have to restart (or somehow tell) the datanodes to start
> sending block reports to the new master. This can increase failover times
> drastically.
Information from DataNode, including block report, corrupt blocks, and
heartbeat information are synchronized to slaves, though heartbeats
from all datanode are collect and synchnoized together once per 30
seconds. Thus it needn't restart datanode.
> 4. I think we will somehow have to handle the split brain scenario where
> there are two masters running on the same cluster. We have to prevent such a
> case.
We use linux-HA/heartbeat cluster with at least 3 nodes to cover split brain.
> 5. Your future section regarding Backupode looks great.
The nearer to mainline is better :)
> My thinking is that datanodes would have to send block reports/block received
> to all the masters. This reduces the number of masters you can have in your
> system. But it will make the failover times quick and fast. any thoughts?
>
I agree. And I think it is the practical step for namenode to get to
HA. Do you think these information should be sent to Backup Node in
editlog stream?
> The NameNode should forward block reports to BackupNode
> -------------------------------------------------------
>
> Key: HDFS-839
> URL: https://issues.apache.org/jira/browse/HDFS-839
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: name-node
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
>
> The BackupNode (via HADOOP-4539) receives a stream of transactions from
> NameNode. However, the BackupNode does not have block locations of blocks. It
> would be nice if the NameNode can forward all block reports (that it receives
> from DataNodes) to the BackupNode.
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