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From Martin Krasser <>
Subject Re: [DISCUSS] Some thoughts about the architecture of camel
Date Tue, 19 Oct 2010 04:58:29 GMT
  +1 for being fully backwards compatible. I've many projects running on 
Camel 2.x and would like to benefit from Camel 3.x features without 
doing any (bigger) changes.
+1 for making a bigger refactoring when going for a more idiomatic Scala 
(DSL) support (with more idiomatic I mean more FP-style e.g. higher 
order functions as combinators in the DSL etc.)

I think it might be useful if we're going to write some more load- and 
stress tests for more frequently used Camel components (jetty, jms etc.) 
and camel-core and run them on a weekly basis, for example. This is not 
only to ensure correct behaviour under load: I've also had several 
customers in the past that where asking for performance numbers. I know 
that performance numbers make most sense for complete applications, but 
having a reference for individual application parts (e.g. raw throughput 
of jetty consumer endpoints) can be useful as well. It would also allow 
us to detect performance decreases more easily (e.g. after refactorings).

Am 19.10.10 06:23, schrieb Claus Ibsen:
> Hi
> I think the idea is really great, but I think the timing for this is
> *not* the right spot.
> And by saying that I mean the goal of Camel 3.0 is to have a short
> development cycle (not like 2.0 which took a long time).
> And as a minimum (IMHO):
> - To upgrade to JDK 1.6+,
> - Spring 3.0+,
> - To optimize the router internally,
> - And to switch to slf4j logger (*)
> - Keeping backwards compatibility as much as possible with 2.x is paramount
> Switching to slf4j instead of commons logging, allows us to use the
> MDC logging feature.
> This allows us to push information to the logs such as message id,
> transaction id etc. which can more easily correlate logs, not only
> with Camel alone, but also with other projects such as ActiveMQ, SMX
> etc.
> On top of that we now have many 3rd party projects which integrate out
> of the box with Camel, so changing the package structure in camel-core
> will break their integration. Which means they may not take up the
> effort to support both Camel 2.x/3.x.
> However I do think we should take the effort and pick up the low
> hanging fruits. I am sure there could be a couple of tangles which can
> be identified and fixed in Camel 3.0, without breaking backwards
> compatibility.
> I think doing this is something for Camel 4 or 5 or 6 (or whatever
> future version it may be) when or if we change to use Scala and use
> some other framework as foundation. There are cool stuff being
> developed for ActiveMQ 6 which are potential as a backbone for route
> messages. And it has a much better threading model which Camel can
> benefit as well.
> Anyway practical works beats theory, so setting up a branch in the
> sandbox to do experiments is a great idea.
> But its very important that we keep backwards compatibility with Camel
> 3.0. There are so many people started using Camel 2.x now so we should
> keep them happy with an easy upgrade path. Eg Camel 3.0 is just like
> 2.x but now on JDK 1.6 and with X other internal upgrades.
> Okay my first cup of coffee is ready, so beware this mail was written
> before I got "my first fix".
> On Mon, Oct 18, 2010 at 7:28 PM, Hadrian Zbarcea<>  wrote:
>> I changed the thread name to [discuss].
>> I like that idea and it's something we contemplated in the past. This will bring
back the idea of getting the dsl out of core as well.
>> What I'd propose Christian is to add your proposal to the roadmap [1]. I will do
the same for the dsl idea. There at least 2 ideas for dsl's built on top of the camel dsl
(scheduling and debugging) that make me even more interested in coming up with a better solution.
>> Once we get some traction on the main refactoring ideas I'd suggest starting one
(or more) branches and start hacking, because there's not a whole lot of time left if we want
to meet our target.
>> Cheers,
>> Hadrian
>> [1]
>> On Oct 18, 2010, at 5:43 AM, Schneider Christian wrote:
>>> Hi all,
>>> I will have some free time in december as I am changing my employer. So I am
planning to work a little on some architectural improvements for camel 3.0.0. As these things
are very critical to the stability of camel I would like to get feedback before I start any
substantial work.
>>> As you surely know currently camel-core is quite tangled. So it is quite difficult
where to start. Some time ago I proposed some improvements to simply reduce those dependency
cycles. As I now know a lot more about camel I think that this simple aproach will not really
work. So this time I want to do this a little more structured. So I start with two simple
>>> "The camel components should know as little as possible about camel core"
>>> "The classes needed to setup camel should be separate from the things needed
at run time"
>>> So why should this be important? Currently components depend on camel-core as
a whole and there are no further rules which classes the components should use and which classes
should be private to core. Even classes from the impl package are needed. So this means that
any refactoring we do in camel core could affect all components. As camel is growing steadily
this can become quite problematic.
>>> So my idea would be to split camel-core into three parts:
>>> api, builder, impl
>>> These should be structured in a way that these big building blocks do not have
cyclic dependencies. Any other cycles can be ignored in this step.
>>> As allowed depdencies I propose ( "->" means may use, depends on):
>>> * ->  api
>>> end user config ->  builder
>>> builder ->  impl
>>> I think the first thing we should do is to discuss and reach a consensus about
a basic architecure and rules like above. Then the next step is to assign each package of
core to one of the basic parts. Then the next step is to resolve cycles between the parts.
>>> What do you think about these ideas?
>>> Thanks
>>> Christian
>>> Christian Schneider
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Martin Krasser


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