Multi-hop query support

[em3s]

Background

EdgeIndex uses narrow rows, requiring N scan API calls for the 2nd hop in multi-hop queries. A wide row structure is introduced to enable multi-get and resolve this. A process to prevent fat rows is also introduced alongside.

Extending from independent per-feature edge queries to cross-feature graph traversal (Unified Graph).

Task

• Phase 0: Design alignment with core model via skeleton E2E
  [1/4] Multi-hop query: skeleton E2E #217
• Phase 1: Mutation + multi-get query to verify (not n-hop yet)
• Phase 2: Query - 2-hop or more
• Phase 3: Server with E2E from Phase 0
• Phase 4: Pruner (fat row prevention)

Done When

• Design alignment based on skeleton
• 2-hop query works in 1+1 API calls
• E2E tests pass

Notes

• Implement n-hop generalization

[zipdoki]

@em3s
I think I can start with a PR from Phase 0. I will let you know once the PR is open!

[zipdoki]

@em3s
The Phase 0 PR is up: #217
It introduces the skeleton E2E for the multi-hop query path along with the EdgeCache model.