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https://issues.apache.org/jira/browse/HDFS-1073?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12930238#action_12930238
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Sanjay Radia commented on HDFS-1073:
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> if anyone may ask for a roll - ie CN, BN, or NN. ...
This is a little ambiguous. Let's clarify:
* Longer Term - we may need to some time to get here since we want to minimize
the changes to the BNN protocol.
** An admin can ask for a roll.
** NN does a roll when the size of the edits is big - say every 10K operations
(a configurable parameter).
** A NewCheckpointer which is given a set of fsimages and edits and it creates
a new checkpointed fsimage. The new fsimage is then copied OFFLINE to the NN,
or wherever else we want it (say NFS, or HDFS). ie there is NO protocol between
the NN and the NewCheckpointer. When this NewCheckpointer is available we can
deprecate the old CheckpointNN (CN).
** BNN does NOT ask for a roll - it simply observes the rolls by the "roll
transaction". - Does this work or have I misunderstood the
design of the BNN?
* Shorter term (ie this Jira and release 22)
** An admin can ask for a roll
** NN does a roll when the size of the edits is big - say every 10K operations
(a configurable parameter).
** BNN can ask for roll since this is already part of the protocol -- btw if
this can be avoided in this jira then good but it may be too much change.
** The CN (really a variation of the BNN) can ask for a roll.
> Simpler model for Namenode's fs Image and edit Logs
> ----------------------------------------------------
>
> Key: HDFS-1073
> URL: https://issues.apache.org/jira/browse/HDFS-1073
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Sanjay Radia
> Assignee: Todd Lipcon
> Attachments: hdfs-1073.txt, hdfs1073.pdf
>
>
> The naming and handling of NN's fsImage and edit logs can be significantly
> improved resulting simpler and more robust code.
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