Open Stack

On Tue, Sep 23, 2014 at 9:13 AM, Zane Bitter <zbitter at redhat.com> wrote:

> On 22/09/14 22:04, Joe Gordon wrote:
>
>> To me this is less about valid or invalid choices. The Zaqar team is
>> comparing Zaqar to SQS, but after digging into the two of them, zaqar
>> barely looks like SQS. Zaqar doesn't guarantee what IMHO is the most
>> important parts of SQS: the message will be delivered and will never be
>> lost by SQS.
>>
>
> I agree that this is the most important feature. Happily, Flavio has
> clarified this in his other thread[1]:
>
>  *Zaqar's vision is to provide a cross-cloud interoperable,
>   fully-reliable messaging service at scale that is both, easy and not
>   invasive, for deployers and users.*
>
>   ...
>
>   Zaqar aims to be a fully-reliable service, therefore messages should
>   never be lost under any circumstances except for when the message's
>   expiration time (ttl) is reached
>
> So Zaqar _will_ guarantee reliable delivery.
>
>  Zaqar doesn't have the same scaling properties as SQS.
>>
>
> This is true. (That's not to say it won't scale, but it doesn't scale in
> exactly the same way that SQS does because it has a different architecture.)
>
> It appears that the main reason for this is the ordering guarantee, which
> was introduced in response to feedback from users. So this is clearly a
> different design choice: SQS chose reliability plus effectively infinite
> scalability, while Zaqar chose reliability plus FIFO. It's not feasible to
> satisfy all three simultaneously, so the options are:
>
> 1) Implement two separate modes and allow the user to decide
> 2) Continue to choose FIFO over infinite scalability
> 3) Drop FIFO and choose infinite scalability instead
>
> This is one of the key points on which we need to get buy-in from the
> community on selecting one of these as the long-term strategy.
>
>  Zaqar is aiming for low latency per message, SQS doesn't appear to be.
>>
>
> I've seen no evidence that Zaqar is actually aiming for that. There are
> waaay lower-latency ways to implement messaging if you don't care about
> durability (you wouldn't do store-and-forward, for a start). If you see a
> lot of talk about low latency, it's probably because for a long time people
> insisted on comparing Zaqar to RabbitMQ instead of SQS.
>

I thought this was why Zaqar uses Falcon and not Pecan/WSME?

"For an application like Marconi where throughput and latency is of
paramount importance, I recommend Falcon over Pecan."
https://wiki.openstack.org/wiki/Zaqar/pecan-evaluation#Recommendation

Yes that statement mentions throughput as well, but it does mention latency
as well.


>
> (Let's also be careful not to talk about high latency as if it were a
> virtue in itself; it's simply something we would happily trade off for
> other properties. Zaqar _is_ making that trade-off.)
>
>  So if Zaqar isn't SQS what is Zaqar and why should I use it?
>>
>
> If you are a small-to-medium user of an SQS-like service, Zaqar is like
> SQS but better because not only does it never lose your messages but they
> always arrive in order, and you have the option to fan them out to multiple
> subscribers. If you are a very large user along one particular dimension (I
> believe it's number of messages delivered from a single queue, but probably
> Gordon will correct me :D) then Zaqar may not _yet_ have a good story for
> you.
>
> cheers,
> Zane.
>
> [1] http://lists.openstack.org/pipermail/openstack-dev/2014-
> September/046809.html
>
>
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