storage: replace DeepEqual in (*EvalResult) MergeAndDestroy

[tbg]

DeepEqual is slow and it should be replaced by a new method (*EvalResult).IsZero (which has an appropriate test and won't rot as we add fields to EvalResult or its substructs).

[a6802739]

@tschottdorf I could do this.

[tbg]

Thanks @a6802739, all yours!

[bdarnell]

We could use the gogoproto.equal option to generate a comparison function for ReplicatedEvalResult. Then we'd only need a hand-written IsZero function for the EvalResult struct (which only has three fields).

Alternately, the reason we can't use the == operator for ReplicatedEvalResult is the fact that it contains start_key and end_key fields (of type roachpb.Key). These fields also take up a lot of space, as reported in #16075. If we could figure out a way to get rid of these fields (perhaps replacing them with a range descriptor sequence number as mentioned in #16075 (comment)), we could go back to using ==.

[a6802739]

@bdarnell , how could I use protoc command to generate *.pb.go file for *.proto file?

[jordanlewis]

@a6802739, we have a Makefile target for that: make protobuf.