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https://issues.apache.org/jira/browse/HDFS-12977?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16520712#comment-16520712
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Erik Krogen commented on HDFS-12977:
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[~vagarychen] I think this is not necessary. By the time the RPC response is
returned to the client, the transaction must have been written to the edit log,
so it will be included in {{getLastWrittenTransactionId()}}. We want to return
as low of an ID as possible because this means less wait time on the Observer
to catch up to the given ID. I think there may be some confusion - IIUC this
{{getLastWrittenTransactionId()}} will be fetched on the _active_, not the
standby, and used as the ID we need to wait for to be caught up.
> 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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