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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9194) RPC Support for QoS
Date Thu, 10 Jan 2013 01:46:13 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9194?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13549281#comment-13549281
] 

Colin Patrick McCabe commented on HADOOP-9194:
----------------------------------------------

Hi Luke,

Interesting idea.  

You mention DiffServ (internet protocol differentiated services) in your description.  Is
there a reason we need our own fields, if the same information is present in DiffServ?  It
seems like if the switch hardware supports DiffServ, it is unnecessary to have our own field
in the RPC header.  On the other hand, if the hardware doesn't support DiffServ, adding our
own byte will do no good.  Am I missing something here?

(Note that I'm not arguing against having QoS-related fields in general in protobuf messages,
just questioning whether it makes sense to put them in the RPC header.)
                
> RPC Support for QoS
> -------------------
>
>                 Key: HADOOP-9194
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9194
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: ipc
>    Affects Versions: 2.0.2-alpha
>            Reporter: Luke Lu
>
> One of the next frontiers of Hadoop performance is QoS (Quality of Service). We need
QoS support to fight the inevitable "buffer bloat" (including various queues, which are probably
necessary for throughput) in our software stack. This is important for mixed workload with
different latency and throughput requirements (e.g. OLTP vs OLAP, batch and even compaction
I/O) against the same DFS.
> Any potential bottleneck will need to be managed by QoS mechanisms, starting with RPC.

> How about adding a one byte DS (differentiated services) field (a la the 6-bit DS field
in IP header) in the RPC header to facilitate the QoS mechanisms (in separate JIRAs)? The
byte at a fixed offset (how about 0?) of the header is helpful for implementing high performance
QoS mechanisms in switches (software or hardware) and servers with minimum decoding effort.

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