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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1975) HA: Support for sharing the namenode state from active to standby.
Date Mon, 28 Nov 2011 04:06:40 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13158168#comment-13158168
] 

Todd Lipcon commented on HDFS-1975:
-----------------------------------

Another issue that we have to tackle before this can provide hot standby is this:

When we close a file, or add another block to a file, we write OP_CLOSE or OP_ADD in the txn
log. FSEditLogLoader, when it sees these types of transactions, creates new BlockInfo objects
for all of the blocks listed in the transaction. These new BlockInfos have no block locations
associated. So, when we close a file, the SBNN loses its block locations info for that file
and is no longer "hot".

I have an ugly hack which copies over the old BlockInfos from the existing INode, but I'm
not convinced it's the right way. It might be cleaner to add new opcode types like OP_ADD_ADDITIONAL_BLOCK,
and actually treat OP_CLOSE as just a finalization of INodeFileUnderConstruction to INodeFile,
rather than replacing block info at all.

Thoughts?
                
> HA: Support for sharing the namenode state from active to standby.
> ------------------------------------------------------------------
>
>                 Key: HDFS-1975
>                 URL: https://issues.apache.org/jira/browse/HDFS-1975
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>            Reporter: Suresh Srinivas
>            Assignee: Jitendra Nath Pandey
>         Attachments: HDFS-1975-HA.2.patch, HDFS-1975-HA.patch, HDFS-1975-HDFS-1623.patch,
HDFS-1975-HDFS-1623.patch, HDFS-1975-HDFS-1623.patch, hdfs-1975.txt, hdfs-1975.txt
>
>
> To enable hot standby namenode, the standby node must have current information for -
namenode state (image + edits) and block location information. This jira addresses keeping
the namenode state current in the standby node. To do this, the proposed solution in this
jira is to use a shared storage to store the namenode state. 
> Note one could also build an alternative solution by augmenting the backup node. A seperate
jira could explore this.

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