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From Jeremy Davis <jerdavis.cassan...@gmail.com>
Subject Re: Creating a Total Ordered Queue in Cassandra
Date Fri, 02 Apr 2010 04:43:36 GMT
You are correct, it is not a queue in the classic sense... I'm storing the
entire "conversation" with a client in perpetuity, and then playing it back
in the order received.

Rabbitmq/activemq etc all have about the same throughput 3-6K persistent
messages/sec, and are not good for storing the conversation forever... Also
I can easily scale cassandra past that message rate and not have to worry
about which message broker/cluster I'm connecting to/has the
conversation/etc.



On Thu, Apr 1, 2010 at 7:02 PM, Keith Thornhill <keith@raptr.com> wrote:

> you mention never deleting from the queue, so what purpose is this
> serving? (if you don't pop off the front, is it really a queue?)
>
> seems if guaranteed order of messages is required, there are many
> other projects which are focused towards that problem (rabbitmq,
> kestrel, activemq, etc)
>
> or am i misunderstanding your needs here?
>
> -keith
>
> On Thu, Apr 1, 2010 at 6:32 PM, Jeremy Davis
> <jerdavis.cassandra@gmail.com> wrote:
> > I'm in the process of implementing a Totally Ordered Queue in Cassandra,
> and
> > wanted to bounce my ideas off the list and also see if there are any
> other
> > suggestions.
> >
> > I've come up with an external source of ID's that are always increasing
> (but
> > not monotonic), and I've also used external synchronization to ensure
> only
> > one writer to a given queue. And I handle de-duping in the app.
> >
> >
> > My current solution is : (simplified)
> >
> > Use the "QueueId", to Key into a row of a CF.
> > Then, every column in that CF corresponds to a new entry in the Queue,
> with
> > a custom Comparator to sort the columns by my external ID that is always
> > increasing.
> >
> > Technically I never delete data from the Queue, and I just page through
> it
> > from a given ID using a SliceRange, etc.
> >
> > Obviously the problem being that the row needs to get compacted. so then
> I
> > started bucketizing with multiple rows for a given queue (for example one
> > per day (again I'm simplifying))...(so the Key is now "QueueId+Day"...)
> >
> > Does this seem reasonable? It's solvable, but is starting to seem
> > complicated to implement... It would be very easy if I didn't have to
> have
> > multiple buckets..
> >
> >
> >
> > My other thought is to store one entry per row, and perform
> get_range_slices
> > and specify a KeyRange, with the OrderPreservingPartitioner.
> > But it isn't exactly clear to me what the Order of the keys are in this
> > system, so I don't know how to construct my key and queries
> appropriately...
> > Is this Lexical String Order? Or?
> >
> > So for example.. Assuming my QueueId's are longs, and my ID's are also
> > longs.. My key would be (in Java):
> >
> > long queueId;
> > long msgId;
> >
> > key = "" + queueId + ":" + msgId;
> >
> > And if I wanted to do a query my key range might be from
> > start = "" + queueId + ":0"
> > end = "" + queueId + ":" + Long.MAX_VALUE;
> >
> > (Will I have to left pad the msgIds with 0's)?
> >
> > And is this going to be efficient if my msgId isn't monotonically
> > increasing?
> >
> > Thanks,
> > -JD
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
>

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