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From "Luke Lu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9194) RPC Support for QoS
Date Fri, 11 Jan 2013 18:56:13 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9194?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13551391#comment-13551391
] 

Luke Lu commented on HADOOP-9194:
---------------------------------

You can use port to differentiate services for IP connections, which essentially communicates
the service class out of band by convention. This is a reasonable hack for internal use (a
la HDFS-599) due to lack of support in the RPC itself. Things quickly get out of hand if we
have more service classes and/or different transport mechanisms without ports (say, again,
unix domain socket (use another file naming convention?)) let alone support for proxy, load
balancing and firewalls.

If we want use Hadoop RPC as general purpose DFS (or computing) client protocols, it needs
to support QoS natively. Having well defined QoS semantics in the RPC also lends to common
libraries of QoS algorithms that can be easily adopted at every necessary layer of our software
stack.
                
> 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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