Add comprehensive documentation comparing the two scaling dimensions:
- Core distinction: N-change is lightweight (rendezvous hash), S-change is heavy (dual-hash dual-write)
- Node scaling moves only ~1/N of documents; resharding affects 100% with 2× transient amplification
- Decision matrix for operators to choose the right approach
- Capacity planning guidance with S = max_nodes_per_group_ever × 8 formula
- References to existing benchmarks and CLI schedule guidance
This completes the remaining work for OP#3 by documenting the trade-offs
so operators understand when to use resharding vs adding nodes.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Bead-Id: bf-jap1
14 chaos tests validate shard migration write safety at every cutover
boundary. Key findings:
- AE on + delta pass: 0/1M loss (production default)
- AE off + delta pass: 0/50K loss (delta pass is sufficient alone)
- AE off + delta skipped: ~2% loss → hard refusal at config validation
- 3-node cluster cutover: 0 loss with delta pass
Hard-coded policy: MigrationCoordinator refuses migrations when both
anti-entropy is disabled and delta pass is skipped. Warning logged when
AE is disabled but delta pass remains active.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
