hi Jorge, I have some thoughts / questions on your arguments against use of the monorepo:
1. If the purpose of Ballista is to support multiple language executors, what does segregating it from the other PL's (where executors are being developed, too) serve to facilitate this goal? 2. Use of the monorepo does not require a synchronized release cycle, just as Rust does not require it now either. The only reason there have not been independent Rust releases is because someone has not volunteered to do it. Likewise, if DataFusion and Ballista are in the same git repository, they don't have to release at the same time as the core arrow / parquet crates. 3. On an incremental basis, I do not believe the increased complexity is significant. A multi-repository setup can be actively worse when development work involves both repositories at the same time. This can be mitigated by pinning the arrow / parquet crates as you point out, but that creates other issues. 4. Even without Jira, there is still the expectation for contributors to communicate in a way that is compatible with the Apache Way. So even without Jira, PMCs have an obligation to establish an alternative structure to have consistently open dialogue / planning about what people are working on or planning to work on in the future. If contributors are extensively discussing / planning privately, these discussions must be moved into the open, whether with design documents or issues or e-mail discussions. This was discussed ad nauseam in the other thread so I won't rehash those arguments. Aside from these issues, the biggest lost opportunity I see if DF/Baliista "cast away" as it were, is that it becomes unattractive for the rest of us to build anything on top of these platforms (because at that point we have a circular dependency, which is the hellscape we escaped from with Parquet C++). I used the datafusion-python project as an example — if that were in the Arrow project I might consider using it in various ways or contribute to it, but as an external project it's less interesting to me as something to build on. On Wed, Mar 10, 2021 at 12:13 PM Jorge Cardoso Leitão <jorgecarlei...@gmail.com> wrote: > > Hi, > > First of all, I want to thank you very much for your work on Ballista and > for doing it in an open source environment. It is something that should be > emphasised and celebrated. > > Secondly, wrt to considering donating it to the Apache Foundation and > Apache project in particular, I would say that we should be honored by such > consideration. In this context, my immediate reaction is: how can we best > support Ballista's community? > > My initial thoughts in this direction are: > > * create a new git repo for DataFusion and Ballista to reside on (e.g. > arrow/ballista) > * do not require the release cycle and versioning to be aligned with > arrow's release cycle > * do not require the usage of JIRA > * pin the dependency of Datafusion on Arrow and parquet crate (e.g. to a > specific commit) > > I feel that this setup would keep Ballista under the Foundation and Apache > Arrow's umbrella and aligned with its goals, while at the same time put the > least amount of burden on its community, both in terms of keeping a strict > release schedule, tooling and CI. > > The rationale for the above is that whenever something is released on > DataFusion (which hosts most of the physical ops), people will also want it > quickly available on Ballista. Thus, having the two release cycles more > closely related and independent of the arrow implementation's cycle is > good. DataFusion does not have integration tests against other arrow > implementations, and thus the integration tests are not relevant. > > There are 4 main reasons I would not recommend placing it in the mono-repo: > > 1. It would not add much > 2. It would place Ballista on the same release schedule and git system as > the rest of Arrow's implementation, which may not suit Ballista's own > development pace (in either direction) > 3. It further increases the complexity of the current repo > 4. It would force its community to use JIRA, merge process, components, > etc, which may not be what its community wishes for > > The main risk I see is that because arrow's release cycle is slow and major > releases only, DataFusion risks missing arrow features from time to time. > We can mitigate this with cargo and pins to commit hashes. IMO this risk > exists in any dependency relationship and is usually a sign that there is > an API contract and thus a trust relationship involved, which is a good > thing. > > Best, > Jorge > > On Tue, Mar 9, 2021 at 6:31 PM Andy Grove <andygrov...@gmail.com> wrote: > > > As many of you know, the reason that I got involved in Arrow back in 2018 > > was that I wanted to build a distributed compute platform in Rust, with > > capabilities similar to Apache Spark. This led to the creation of the > > DataFusion query engine, which is an in-memory query engine and is now part > > of the Arrow repo. > > > > Over the past couple of years, I have been working outside of Arrow on a > > project named “Ballista” [1] to continue the journey of trying to build a > > distributed version. Due to the pandemic, I have had time over the winter > > to put more effort into this project and have managed to build a small > > community around it over the past few months and the project has now > > reached a point where the basic architecture has been proven and it is now > > getting a lot of attention (more than 2k stars on GitHub just recently) and > > I think that it would now make sense to donate some or all of the project > > to Apache Arrow and continue its growth here. > > > > For an overview of the project, please see the talk I recently gave at the > > New York Open Statistical Programming Meetup [2]. > > > > Some of the benefits that I see in donating the project to Arrow are: > > > > > > - > > > > DataFusion also needs a scheduler and it would probably make sense to > > push some parts of the Ballista scheduler down a level in the stack so > > that > > the same approach is used to scale across cores in DataFusion and to > > scale > > across nodes in Ballista. > > - > > > > Ballista provides preliminary support for spill-to-disk functionality > > (in Arrow IPC format) which could also benefit DataFusion and provide > > better scalability through out-of-core processing. > > - > > > > Although the Ballista scheduler is implemented in Rust, it is possible > > to implement executors in other languages due to the use of Flight, > > gRPC, > > and protobuf, so this may be of interest to other language > > implementations > > of Arrow as well. > > - > > > > There is already some overlap between Arrow and Ballista contributors. > > - > > > > Ballista unit tests will be part of Arrow CI which means that any > > changes to Arrow or DataFusion APIs that Ballista depends on will also > > require that the corresponding Ballista code is updated as part of the > > same > > PR. > > > > > > My main goal with this email thread is to gauge interest in donating this > > code. If there is interest in doing so then we can have a more detailed > > follow-up conversation on exactly what would be donated and where it would > > go. > > > > > > I have also filed a GitHub issue in Ballista to get feedback from current > > contributors [3]. > > > > > > I'm looking forward to hearing opinions on this! > > > > > > Thanks, > > > > Andy. > > > > [1] https://github.com/ballista-compute/ballista > > > > [2] https://www.youtube.com/watch?v=ZZHQaOap9pQ > > > > [3] https://github.com/ballista-compute/ballista/issues/646 > >
