Allow ability to set context deadline for GRPC calls

[emhagman]

See:
https://github.com/tony612/grpc-elixir/blob/b635aff233e8db173557e9eca414bc9d640e71d7/test/grpc/integration/stub_test.exs

Also see:
https://discuss.dgraph.io/t/dgraph-java-client-setting-deadlines-per-call/3056

And also why we should be able to pass it in:
https://grpc.io/blog/deadlines

[ospaarmann]

Hey,

this makes sense to me. For me personally it makes more sense to focus first on supporting transactions. But if you want to enable context deadlines, feel free to submit a PR. I would just ask you to

• outline here how you plan to do it
• make it configurable and make sure, that the naming is not confusing (we already have :timeout which holds the value for the connection timeout)

Thanks!
Ole

[emhagman]

I agree I'd probably want to see transaction support first as well but I'll give this a shot.

[ospaarmann]

@emhagman I sometimes get the error

{:error, [code: 2, message: "While proposing: context deadline exceeded"]}

back from Dgraph. So a context deadline is already set but not explicitly. This seems to be a performance issue and goes away when I reset Dgraph by deleting all data. So setting this explicitly from ExDgraph seems to be a very good idea 😉

[emhagman]

See #24