Devise means of indicating which fields should be indexed

[Jason-Abbott]

Indexing means creating a separate set of key-values where the field to be indexed becomes the (lexicographically sorted) key and the value it points to is the actual key of the full Protobuf message. That overhead means we probably don't want to do it for every field.

[Jason-Abbott]

These can be implemented as proto standard field options. See for example GoGo's option extensions.