[jira] [Commented] (HDFS-16696) NameNode supports a new MsyncRPCServer to handle msync() RPC separately

["Erik Krogen (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-16696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17572023#comment-17572023 ] 

Erik Krogen commented on HDFS-16696:
------------------------------------

Generally +1 from me as long as we can get it done without introducing too much additional complexity, and keep it off-by-default. If we assume there are many clients using always-msync mode (including for Design B laid out in HDFS-13522), then latency of msync ops becomes very critical. Even without always-msync mode, latency of msync can have an impact on performance, so it's still potentially useful.

> NameNode supports a new MsyncRPCServer to handle msync() RPC separately
> -----------------------------------------------------------------------
>
>                 Key: HDFS-16696
>                 URL: https://issues.apache.org/jira/browse/HDFS-16696
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: ZanderXu
>            Assignee: ZanderXu
>            Priority: Major
>
> HDFS-12943 introduced Consistent Reads from Standby Node. It use msync mechanism to guarantee the consistency.  So the latency of msycn() rpc is very important, especially for some end users who need call msync() rpc every time.
> Unfortunately, NameNode handle msync() RPCs same with other RPCs, also need enqueue, wait, handled. So the msync() will be blocked by other RPCs, such as setQuota, rename, delete, etc. 
> So we need a new mechanism to guarantee the latency of the msync() RPC.
> Such as: 
> * We can supports a new MsyncRPCServer in NameNode to separately msync() RPC.



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