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From Matei Zaharia <matei.zaha...@gmail.com>
Subject Re: [VOTE] Designating maintainers for some Spark components
Date Thu, 06 Nov 2014 01:50:16 GMT
Hi Tim,

We can definitely add one for that if the component grows larger or becomes harder to maintain.
The main reason I didn't propose one is that the Mesos integration is actually a lot simpler
than YARN at the moment, partly because we support several YARN versions that have incompatible
APIs. But so far our modus operandi has been to ask Mesos contributors to review patches that
touch it.

We didn't want to add a lot of components at the beginning partly to minimize overhead, but
we can revisit it later. It would definitely be bad if we break Mesos support.

Matei

> On Nov 5, 2014, at 5:35 PM, Timothy Chen <tnachen@gmail.com> wrote:
> 
> Hi Matei,
> 
> Definitely in favor of moving into this model for exactly the reasons
> you mentioned.
> 
> From the module list though, the module that I'm mostly involved with
> and is not listed is the Mesos integration piece.
> 
> I believe we also need a maintainer for Mesos, and I wonder if there
> is someone that can be added to that?
> 
> Tim
> 
> On Wed, Nov 5, 2014 at 5:31 PM, Matei Zaharia <matei.zaharia@gmail.com> wrote:
>> Hi all,
>> 
>> I wanted to share a discussion we've been having on the PMC list, as well as call
for an official vote on it on a public list. Basically, as the Spark project scales up, we
need to define a model to make sure there is still great oversight of key components (in particular
internal architecture and public APIs), and to this end I've proposed implementing a maintainer
model for some of these components, similar to other large projects.
>> 
>> As background on this, Spark has grown a lot since joining Apache. We've had over
80 contributors/month for the past 3 months, which I believe makes us the most active project
in contributors/month at Apache, as well as over 500 patches/month. The codebase has also
grown significantly, with new libraries for SQL, ML, graphs and more.
>> 
>> In this kind of large project, one common way to scale development is to assign "maintainers"
to oversee key components, where each patch to that component needs to get sign-off from at
least one of its maintainers. Most existing large projects do this -- at Apache, some large
ones with this model are CloudStack (the second-most active project overall), Subversion,
and Kafka, and other examples include Linux and Python. This is also by-and-large how Spark
operates today -- most components have a de-facto maintainer.
>> 
>> IMO, adopting this model would have two benefits:
>> 
>> 1) Consistent oversight of design for that component, especially regarding architecture
and API. This process would ensure that the component's maintainers see all proposed changes
and consider them to fit together in a good way.
>> 
>> 2) More structure for new contributors and committers -- in particular, it would
be easy to look up who’s responsible for each module and ask them for reviews, etc, rather
than having patches slip between the cracks.
>> 
>> We'd like to start with in a light-weight manner, where the model only applies to
certain key components (e.g. scheduler, shuffle) and user-facing APIs (MLlib, GraphX, etc).
Over time, as the project grows, we can expand it if we deem it useful. The specific mechanics
would be as follows:
>> 
>> - Some components in Spark will have maintainers assigned to them, where one of the
maintainers needs to sign off on each patch to the component.
>> - Each component with maintainers will have at least 2 maintainers.
>> - Maintainers will be assigned from the most active and knowledgeable committers
on that component by the PMC. The PMC can vote to add / remove maintainers, and maintained
components, through consensus.
>> - Maintainers are expected to be active in responding to patches for their components,
though they do not need to be the main reviewers for them (e.g. they might just sign off on
architecture / API). To prevent inactive maintainers from blocking the project, if a maintainer
isn't responding in a reasonable time period (say 2 weeks), other committers can merge the
patch, and the PMC will want to discuss adding another maintainer.
>> 
>> If you'd like to see examples for this model, check out the following projects:
>> - CloudStack: https://cwiki.apache.org/confluence/display/CLOUDSTACK/CloudStack+Maintainers+Guide
<https://cwiki.apache.org/confluence/display/CLOUDSTACK/CloudStack+Maintainers+Guide>
>> - Subversion: https://subversion.apache.org/docs/community-guide/roles.html <https://subversion.apache.org/docs/community-guide/roles.html>
>> 
>> Finally, I wanted to list our current proposal for initial components and maintainers.
It would be good to get feedback on other components we might add, but please note that personnel
discussions (e.g. "I don't think Matei should maintain *that* component) should only happen
on the private list. The initial components were chosen to include all public APIs and the
main core components, and the maintainers were chosen from the most active contributors to
those modules.
>> 
>> - Spark core public API: Matei, Patrick, Reynold
>> - Job scheduler: Matei, Kay, Patrick
>> - Shuffle and network: Reynold, Aaron, Matei
>> - Block manager: Reynold, Aaron
>> - YARN: Tom, Andrew Or
>> - Python: Josh, Matei
>> - MLlib: Xiangrui, Matei
>> - SQL: Michael, Reynold
>> - Streaming: TD, Matei
>> - GraphX: Ankur, Joey, Reynold
>> 
>> I'd like to formally call a [VOTE] on this model, to last 72 hours. The [VOTE] will
end on Nov 8, 2014 at 6 PM PST.
>> 
>> Matei


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