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From Mike Percy <mpe...@cloudera.com>
Subject Re: Roadmap for v1.1.0
Date Mon, 05 Mar 2012 07:29:53 GMT
On Mar 4, 2012, at 9:52 PM, Juhani Connolly wrote:

> In the "poor code reviews" discussion, Mike Percy suggested opening up a thread regarding
the roadmap for 1.1.0 and beyond, so here's a go at kicking that off.
> 
> I think a the following questions present themselves, along with my opinions:
> 
> - When do we hope to make the next solid release? Do we have a planned schedule(that
I may be unaware of?)
> Personally I am not too attached to deciding a date in advance and would prefer to decide
a fixed set of issues that we prioritize to fix, then limit the branch to bug fixes only(moving
any further dev to a separate branch), and push that out as the next release when sufficient
testing has been made with harmful bugs removed.

I'd be inclined to try to release as often as we think we have useful features and bug fixes
implemented, to maintain a rhythm and keep the vitality of the project high. I think releasing
often also helps encourage users to engage with the developer community and try out and vet
experimental features.

> - What belongs in 1.1.0?
> I for one think that for any log delivery infrastructure the core parts for delivery
mechanisms and error recovery mechanisms should be of primary importance, and this is what
I've been trying to work on. I do not feel that any further sources or sinks are necessary,
but feel that for delivery mechanisms, the lack of a FileChannel is pretty painful. I also
feel that a buffering mechanism(as in scribed), allowing to store channel overflow in a long-term
medium should be a priority.

I tend agree with what you're saying, although I don't really have an aversion to integrating
more Sinks as long as they have maintainers. I agree that a long term buffering solution is
very important, I think that would be part of FileChannel though. Overall I think we should
strive for correctness in the core, medium term API stability, and system speed, in that order
for the next release. The primary thing I am looking at right now is the RPC mechanism, to
ensure we are set up to take full advantage of Avro RPC performance features and ensure that
remote clients can integrate with Flume in the future. I have some concerns there and I'll
start a thread about it tomorrow probably, since if there are reasons to break wire compatibility
we should do it as early as possible in the life of 1.x. (incidentally I also think we should
start calling it 1.x instead of NG to avoid coining terms like Flume ONG and Flume NNG for
2.x :)

Along the vein of system interfaces, one big thing that I think is missing in Flume is Javadoc
of all the core interfaces and classes. This is something I am certainly willing to work on.
Mainly I believe that the various interface contracts need to be strongly specified in the
base class Javadoc so that it's easier to tell if something is wrong and to ensure consistency
across implementations. For example, if there is an error delivering an event should a Sink
return BACKOFF or throw an EventDeliveryException? I'm not sure why one is a return value
and the other is an exception, but we should make sure consequences and best practices are
documented, and any Sinks in the core should be consistent. I'm still getting my head around
the system and using the source (, Luke) to figure these things out. But hopefully future
devs and API users won't have to do that as much.

One more thing that I think is important, while not really related to a software release per
se, is coming up with stories around how common use cases are supposed to work or eventually
be possible. Something I've been thinking about a lot is Apache web server log collection
onto HDFS. While tail source is known to be problematic (deserves a FAQ entry), we should
provide explanations and best practices for the most common cases. (In this case I think it
involves writing an apache httpd mod_flume module that speaks Avro). We can then eventually
provide code for these most common cases when we have time to implement them or as they are
contributed. These very common use cases and the stories around them should inform our design
decisions.

> I am unsure of configuration overhauls. We have one configuration method that works.
Should a centralized one be an immediate target or one for 1.1.0. Should refactoring the 
configuration be a priority(it was pointed out that FlumeConfiguration has become a god class)?
> There are a few other leftovers from flume-728: metric collection infrastructure, documentation,
master. Should these be targets for 1.1.0 or for further down the road?
> We should probably also make clear which components need to be thread safe and which
don't. We should also verify this is the case.

OK so my understanding is that some changes to how we do config validation are required to
be able to write a tool to validate Flume configs without having to start an agent. The idea
is for this functionality to be separated from the core to some extent so that the validation
mechanism can be exposed as an API. The initial request for an API came from the Cloudera
enterprise team, who wants to add Flume configuration validation support in the Cloudera Manager
app. Personally I think it would be a great feature to have in a command line tool as well.
From an operations perspective, it's nice to have the ability to check that your config is
valid before pushing it, instead of finding out your config is broken once you deploy to all
your agents… especially if you are in an emergency production situation and you need to
make changes fast. If you have concerns about the implementation beyond the issues that Eric
raised, or even if you agree/disagree with the current feedback on the review, then I know
Hari would appreciate any constructive feedback that you or other folks can provide. Of course
if folks think that it's an undesirable feature, have concerns, or think there is a better
way to design it then they should definitely speak up in the JIRA, the review tool, or here
as well.

Anyway, I think other folks should chime in on this thread and we should ultimately morph
this discussion into a list of JIRAs for inclusion into a 1.1.0. And I would advocate that
the rest would move to 1.2.0 by default.

Regards,
Mike


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