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From "Erik Krogen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-13688) Introduce msync API call
Date Mon, 30 Jul 2018 22:48:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-13688?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16562631#comment-16562631
] 

Erik Krogen commented on HDFS-13688:
------------------------------------

Hey [~vagarychen], I think separating out into client- and server-side makes sense. However,
this patch which claims to be only client-side is still making changes to server-side classes
like {{o.a.h.ipc.Server}}, {{GlobalStateIdContext}}. Would it be better to have this as a
part of the server-side change?

That being said, in {{GlobalStateIdContext}}, should we be using {{getCorrectLastAppliedOrWrittenTxId}}
rather than {{getLastAppliedOrWrittenTxId}}, which gets the ID without a lock? This could
result in an older txn ID value being returned. I think we need to take the lock here.

One minor nit, the Javadoc for {{DFSClient#msync()}} should have an empty line before the
{{@throws}}

> Introduce msync API call
> ------------------------
>
>                 Key: HDFS-13688
>                 URL: https://issues.apache.org/jira/browse/HDFS-13688
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Chen Liang
>            Assignee: Chen Liang
>            Priority: Major
>         Attachments: HDFS-13688-HDFS-12943.001.patch, HDFS-13688-HDFS-12943.002.patch,
HDFS-13688-HDFS-12943.002.patch, HDFS-13688-HDFS-12943.003.patch, HDFS-13688-HDFS-12943.004.patch,
HDFS-13688-HDFS-12943.WIP.002.patch, HDFS-13688-HDFS-12943.WIP.patch
>
>
> As mentioned in the design doc in HDFS-12943, to ensure consistent read, we need to introduce
an RPC call {{msync}}. Specifically, client can issue a msync call to Observer node along
with a transactionID. The msync will only return when the Observer's transactionID has caught
up to the given ID. This JIRA is to add this API.



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