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From "Jeremy Hanna (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1485) Add a weighted request scheduler
Date Tue, 21 Sep 2010 16:56:34 GMT


Jeremy Hanna commented on CASSANDRA-1485:

bq Could we attach the weights to the queue to minimize the work done in the scheduling loop?

I agree that we want to minimize instructions in the scheduler.  However, the getWeight method
only does a null check and potentially a hashmap lookup.  If we were to attach weights to
the queue, say make the queue have a Pair<String, Integer> key instead of just a String
key, that might cause a lot more objects (Pairs and Integers) to be created.  Also, it would
still have to call getWeight.  It would just call it in the queue(...) method instead of in
the schedule() loop.  So getWeight would still be called the same number of times - once per
request thread.

bq In the innermost loop, you should probably break the weighted loop if the thread popped
is ever null

true - will add that.

bq The changes in ClientState are not necessary for this patch
They're not necessary for this patch, but it cleans up that method and removes the necessity
for SCHEDULE_ON_KEYSPACE by just doing a switch over the values in that enum.  Changing the
name to SchedulingValue just seemed more intuitive to me as I had been confusing schedulerId
and schedulingId.  It helped me get them straight more easily - maybe that's just me.

> Add a weighted request scheduler
> --------------------------------
>                 Key: CASSANDRA-1485
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>    Affects Versions: 0.7 beta 1
>            Reporter: Jeremy Hanna
>            Assignee: Jeremy Hanna
>            Priority: Minor
>             Fix For: 0.7 beta 2
>         Attachments: 0001-added-basic-keyspace-weighting.patch
> Now that CASSANDRA-1035 has given Cassandra a request scheduler interface, it would be
nice to have a weighted request scheduler.

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