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From Jay Kreps <jay.kr...@gmail.com>
Subject Re: What are the most significant differences between kestrel and kafka?
Date Tue, 09 Oct 2012 15:47:50 GMT
I am not very knowledgeable about Kestrel, but here are the differences I
am aware of:
1. Kafka keeps a single log for any number of subscribers. I think in
Kestrel you need to store each message once per subscriber. This makes
Kafka consumers very very cheap (basically just the bandwidth usage). We
take advantage of this even for "queue" processing to add monitoring
consumers, do an occational ad hoc "tail -f" on the queue and other things
like that.
2. Kestrel does not depend on Zookeeper which means it is operationally
less complex if you don't already have a zk installation.
3. As Even says Kafka has significantly better throughput.
4. Kestrel doesn't support ordered consumption.
5. As Even says, all messages in Kafka use consumer acknowledgement.
Kestrel supports this but it is a more expensive option, and the default is
"at most once delivery".
6. I think the consumer model for Kestrel requires either manually mapping
consumers to specific servers, or randomly load balancing consumers over
servers. Manual configuration is problematic because of the lack of
elasticity: if a server fails some consumers will be underutilized, and if
a consumer fails some server may be unconsumed. This may lead to having
to over-provision your consumers so you can still keep up in the case where
a consumer fails. Randomly load balancing has the problem that due to bad
luck some server will have no consumers for a period of time leading to
poor end-to-end latency and potential problems if the server doesn't handle
large backlog well.



On Mon, Oct 8, 2012 at 9:48 AM, Evan Chan <ev@ooyala.com> wrote:

> Howard,
> The Kafka model is very different from the Kestrel model, at least as far
> as consumers are concerned.
> Kestrel is like AMQP / RabbitMQ in that it keeps track of consumer state,
> and you can individually check out messages, and Kestrel will only remove
> it from the queue when you "commit".   Keeping track of this state slows
> down Kestrel signifiantly though.
> Kafka does not keep track of consumer state.  Each consumer keeps track of
> an "offset" on its own, and load balancing and offset rollbacks are done
> completely in the consumer.   Kafka doesn't support RabbitMQ-style message
> checkout and commit, in the server, although you could in theory implement
> such a consumer yourself.  The benefit, though is that Kafka has very
> little state to track and is wicked fast.
> In production, Kafka throughput easily trumps Kestrel throughput when you
> use the checkout/commit features.
> -Evan
> On Mon, Oct 8, 2012 at 9:08 AM, howard chen <howachen@gmail.com> wrote:
> > Hi,
> >
> > Someone asked in Quora
> > (
> >
> http://www.quora.com/Apache-Kafka/What-are-the-most-significant-differences-between-kestrel-and-kafka
> > )
> > and I found this question is particularly interesting, since not many
> > people has the experience in dealing with these systems.
> >
> > My understanding is as following, so pls correct me if I am wrong:
> >
> > Same:
> > - Both are durable and queue's size is limited by disk storage instead of
> > memory
> > - There are both very fast
> >
> > Difference:
> >
> > - No strict ordering kestrel
> > - Not transactional for kestrel
> > - No unique delivery guarantee for kestrel
> > - No zookeeper coordination for kestrel
> >
> > So it seems to me that kafka is a more complete solution for message
> > streaming solution while kestrel is a simplistic implementation of
> > message queue, am I right?
> >
> > Anything to add?
> > Thanks.
> >
> --
> --
> *Evan Chan*
> Senior Software Engineer |
> ev@ooyala.com | (650) 996-4600
> www.ooyala.com | blog <http://www.ooyala.com/blog> |
> @ooyala<http://www.twitter.com/ooyala>

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