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From "Luke Lu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9194) RPC Support for QoS
Date Sat, 09 Mar 2013 00:49:14 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9194?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13597749#comment-13597749

Luke Lu commented on HADOOP-9194:

bq. Can you explain how this would be used?

At RPC layer it could be used to dispatch request into different queues with different service
priority. The service class can be carried from end-to-end for QoS in any layer that can be
a bottleneck. I think that something similar to [CoDel|https://en.wikipedia.org/wiki/CoDel]
at RPC layer would suffice in common cases without tuning as it incorporates RTT.

bq. is there a reason not to just put this as an optional field in the protobuf messages themselves?

As I mentioned the description, put the field in a fixed header simplify/speed up (soft) switch
implementation, regardless of serialization type. Besides, we should do this when we're doing
compatibility breaking changes mentioned in HADOOP-8990 before it's too late.

> 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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