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From "Chao Sun (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12943) Consistent Reads from Standby Node
Date Tue, 18 Dec 2018 06:37:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12943?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16723757#comment-16723757
] 

Chao Sun commented on HDFS-12943:
---------------------------------

[~brahmareddy] [~xkrogen]: unfortunately I can't provide enough data points on this. In our
production we deployed a slight different version than upstream - the observer hosts are fixed
in config so no {{getHAServiceState}} is issued (on the downside observer cannot participate
in failover). I do intend to run some benchmark with the latest upstream code though. Perhaps
will update later.

> Consistent Reads from Standby Node
> ----------------------------------
>
>                 Key: HDFS-12943
>                 URL: https://issues.apache.org/jira/browse/HDFS-12943
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: hdfs
>            Reporter: Konstantin Shvachko
>            Priority: Major
>         Attachments: ConsistentReadsFromStandbyNode.pdf, ConsistentReadsFromStandbyNode.pdf,
HDFS-12943-001.patch, HDFS-12943-002.patch, TestPlan-ConsistentReadsFromStandbyNode.pdf
>
>
> StandbyNode in HDFS is a replica of the active NameNode. The states of the NameNodes
are coordinated via the journal. It is natural to consider StandbyNode as a read-only replica.
As with any replicated distributed system the problem of stale reads should be resolved. Our
main goal is to provide reads from standby in a consistent way in order to enable a wide range
of existing applications running on top of HDFS.



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