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https://issues.apache.org/jira/browse/HDFS-12977?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16519803#comment-16519803
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Chen Liang commented on HDFS-12977:
-----------------------------------
It seems the name space ID is picked up here by reading
{{namesystem.getLastWrittenTransactionId()}}. I am thinking would it be better
to pick up {{namesystem.getFSImage().getLastAppliedOrWrittenTxId()}} instead?
My understanding is that (please correct me if I'm wrong),
{{getLastWrittenTransactionId()}} returns the last id that has been written to
persistent storage, while {{getLastAppliedOrWrittenTxId()}} returns the last id
that has been written storage, OR has been applied to name space, but not yet
persisted, whichever is larger. I think as long as a change is applied to
Standby in memory namespace, the id can be safely made visible for client to
read, there seems no need to wait longer for it to be persisted here. What do
you think [~shv], [~zero45]?
> Add stateId to RPC headers.
> ---------------------------
>
> Key: HDFS-12977
> URL: https://issues.apache.org/jira/browse/HDFS-12977
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: ipc, namenode
> Reporter: Konstantin Shvachko
> Assignee: Plamen Jeliazkov
> Priority: Major
> Fix For: HDFS-12943
>
> Attachments: HDFS_12977.trunk.001.patch, HDFS_12977.trunk.002.patch,
> HDFS_12977.trunk.003.patch, HDFS_12977.trunk.004.patch,
> HDFS_12977.trunk.005.patch, HDFS_12977.trunk.006.patch,
> HDFS_12977.trunk.007.patch, HDFS_12977.trunk.008.patch
>
>
> stateId is a new field in the RPC headers of NameNode proto calls.
> stateId is the journal transaction Id, which represents LastSeenId for the
> clients and LastWrittenId for NameNodes. See more in [reads from Standby
> design
> doc|https://issues.apache.org/jira/secure/attachment/12902925/ConsistentReadsFromStandbyNode.pdf].
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