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From "Chris Li (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HADOOP-10282) Create a FairCallQueue: a multi-level call queue which schedules incoming calls and multiplexes outgoing calls
Date Wed, 20 Aug 2014 03:27:48 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-10282?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Chris Li updated HADOOP-10282:
------------------------------

    Attachment: HADOOP-10282.patch

Hi [~arpitagarwal] sorry for the delay, I wanted to fix up the tests for more isolation from
the mux and scheduler.

I remember why I made that comment now, it's because poll() without timeunit and peek() don't
acquire the takeLock, so it is possible for poll()/peek() to return null even though something
is in the queue. This doesn't affect hadoop since hadoop uses poll(long, TimeUnit) exclusively.

I wanted to get this patch out asap, but I think it would also be good to have pluggable schedulers
and multiplexers in the FCQ itself, as it enables some cool stuff like HADOOP-10598. I will
open another issue for making pluggable schedulers/muxes.

> Create a FairCallQueue: a multi-level call queue which schedules incoming calls and multiplexes
outgoing calls
> --------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-10282
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10282
>             Project: Hadoop Common
>          Issue Type: Sub-task
>            Reporter: Chris Li
>            Assignee: Chris Li
>         Attachments: HADOOP-10282.patch, HADOOP-10282.patch, HADOOP-10282.patch
>
>
> The FairCallQueue ensures quality of service by altering the order of RPC calls internally.

> It consists of three parts:
> 1. a Scheduler (`HistoryRpcScheduler` is provided) which provides a priority number from
0 to N (0 being highest priority)
> 2. a Multi-level queue (residing in `FairCallQueue`) which provides a way to keep calls
in priority order internally
> 3. a Multiplexer (`WeightedRoundRobinMultiplexer` is provided) which provides logic to
control which queue to take from
> Currently the Mux and Scheduler are not pluggable, but they probably should be (up for
discussion).
> This is how it is used:
> // Production
> 1. Call is created and given to the CallQueueManager
> 2. CallQueueManager requests a `put(T call)` into the `FairCallQueue` which implements
`BlockingQueue`
> 3. `FairCallQueue` asks its scheduler for a scheduling decision, which is an integer
e.g. 12
> 4. `FairCallQueue` inserts Call into the 12th queue: `queues.get(12).put(call)`
> // Consumption
> 1. CallQueueManager requests `take()` or `poll()` on FairCallQueue
> 2. `FairCallQueue` asks its multiplexer for which queue to draw from, which will also
be an integer e.g. 2
> 3. `FairCallQueue` draws from this queue if it has an available call (or tries other
queues if it is empty)
> Additional information is available in the linked JIRAs regarding the Scheduler and Multiplexer's
roles.



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