I recently worked on an issue that had to be implemented in parquet-cpp (ARROW-1644, ARROW-1599) but required changes in arrow (ARROW-2585, ARROW-2586). I found the circular dependencies confusing and hard to work with. For example, I still have a PR open in parquet-cpp (created on May 10) because of a PR that it depended on in arrow that was recently merged. I couldn't even address any CI issues in the PR because the change in arrow was not yet in master. In a separate PR, I changed the run_clang_format.py script in the arrow project only to find out later that there was an exact copy of it in parquet-cpp.
However, I don't think merging the codebases makes sense in the long term. I can imagine use cases for parquet that don't involve arrow and tying them together seems like the wrong choice. There will be other formats that arrow needs to support that will be kept separate (e.g. - Orc), so I don't see why parquet should be special. I also think build tooling should be pulled into its own codebase. GNU has had a long history of developing open source C/C++ projects that way and made projects like autoconf/automake/make to support them. I don't think CI is a good counter-example since there have been lots of successful open source projects that have used nightly build systems that pinned versions of dependent software. That being said, I think it makes sense to merge the codebases in the short term with the express purpose of separating them in the near term. My reasoning is as follows. By putting the codebases together, you can more easily delineate the boundaries between the API's with a single PR. Second, it will force the build tooling to converge instead of diverge, which has already happened. Once the boundaries and tooling have been sorted out, it should be easy to separate them back into their own codebases. If the codebases are merged, I would ask that the C++ codebases for arrow be separated from other languages. Looking at it from the perspective of a parquet-cpp library user, having a dependency on Java is a large tax to pay if you don't need it. For example, there were 25 JIRA's in the 0.10.0 release of arrow, many of which were holding up the release. I hope that seems like a reasonable compromise, and I think it will help reduce the complexity of the build/release tooling. On Mon, Jul 30, 2018 at 8:50 PM Ted Dunning <ted.dunn...@gmail.com> wrote: > On Mon, Jul 30, 2018 at 5:39 PM Wes McKinney <wesmck...@gmail.com> wrote: > > > > > > The community will be less willing to accept large > > > changes that require multiple rounds of patches for stability and API > > > convergence. Our contributions to Libhdfs++ in the HDFS community took > a > > > significantly long time for the very same reason. > > > > Please don't use bad experiences from another open source community as > > leverage in this discussion. I'm sorry that things didn't go the way > > you wanted in Apache Hadoop but this is a distinct community which > > happens to operate under a similar open governance model. > > > There are some more radical and community building options as well. Take > the subversion project as a precedent. With subversion, any Apache > committer can request and receive a commit bit on some large fraction of > subversion. > > So why not take this a bit further and give every parquet committer a > commit bit in Arrow? Or even make them be first class committers in Arrow? > Possibly even make it policy that every Parquet committer who asks will be > given committer status in Arrow. > > That relieves a lot of the social anxiety here. Parquet committers can't be > worried at that point whether their patches will get merged; they can just > merge them. Arrow shouldn't worry much about inviting in the Parquet > committers. After all, Arrow already depends a lot on parquet so why not > invite them in? >
