Partitioning & Load

Core goal

Scale out without losing correctness:

• deterministic key ownership
• balanced runtime load

Layer 1: ownership

Consistent hash ring:

• owner = first token clockwise
• wrap on ring end
• deterministic tie-breaks for duplicate positions

Layer 2: replica placement

Ring walk from owner:

• distinct nodes only
• deterministic order
• prefer failure-domain diversity (zone/rack)

Layer 3: rebalancing

Move shards only when it helps.

Constraints matter:

• move budget
• pinned shards
• monotonic improvement
• oscillation avoidance

Key pitfalls

• repeated replicas on same node/domain
• unstable tie-breaks
• moves that worsen max-min gap
• endless rebalance loops

Exercise progression

1. Ownership resolver
2. Domain-aware replica planner
3. Constrained rebalance capstone