Merge DynamoDB plugin into JanusGraph upstream

[amcp]

I think 0.2.X support is where merging DynamoDB should start to support Titan 1.0.0 compatibility, and then we can cherry-pick that commit and massage it into the 0.3.X series.

[amcp]

@mbrukman

[FlorianHockmann]

Shouldn't we have a discussion first on janusgraph-dev of whether we want to add more backends to JanusGraph in general and whether all new backends should be merged into the main repo or in a separate repo?

[amcp]

@FlorianHockmann this sounds like a good idea. Do you want to start one or should I? We should be open to contributions in general, but this particular ask has been around for a while. I believe it has been discussed and asked for in one of our mailing lists.

[FlorianHockmann]

Yes, we should be open to contributions in general, but a new backend is basically a completely new project that needs to be maintained. If we accept it into JanusGraph, then we also need to maintain it.
I want to avoid a situation where we have a bunch of backends that were donated by contributors who aren't around to maintain them anymore which means more work for the few regular contributors that we currently have.

My point is not directly aimed at the DynamoDB backend, but if we accept that, then why not a Couchbase backend, Ted's FoundationDB backend or backend XY someone developed just for fun?

If we accept a new backend, then it could also be an option to let it live in its own repo. That way, it doesn't slow down our builds and the development process in general.

I think it makes sense if you start the discussion as you want to merge the backend.

[porunov]

I would agree here with @FlorianHockmann .

Also, I think it would be better when all backends would be separate projects. I think they could be hosted in JanusGraph github as separate repositories if they are maintained by someone. Generally, we could have "officially supported backends" (hosted in JanusGraph github) and "third party backends" (hosted not in JanusGraph github).

I agree that discussion is needed.

P.S. I didn't check how current backends are bound to JanusGraph core. So, the above is just my thoughts. I think if they are hard to be separated then we shouldn't move them at least for now. If they are easily separated then it may be better to move them.