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From "Erik Krogen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12977) Add stateId to RPC headers.
Date Fri, 22 Jun 2018 19:25:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12977?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16520712#comment-16520712
] 

Erik Krogen commented on HDFS-12977:
------------------------------------

[~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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