Operation Indexes
An operation index is a freshness token associated with a write. ZoneTree uses it to order writes for the same key when replaying logs, loading in-memory segments, or applying replicated operations.
Per-Key Freshness
The operation index is not a global database timestamp. It matters when comparing operations for the same key.
This distinction is important:
- newer operation for key
Ashould beat older operation for keyA, - operation indexes for unrelated keys do not define the shape of the whole database.
Why It Exists
ZoneTree stores data across multiple layers. During recovery and replication, the engine may need to decide which operation wins for a key. The operation index gives ZoneTree a stable way to preserve the intended write order for that key.
Persisted Segments
Persisted disk segment entries do not need to keep per-entry operation indexes in the same way mutable in-memory segments do. Once data is merged into a disk segment, segment ordering and merge rules carry the durable shape.
Replication And Audit
Operation indexes are useful when building replication, audit, or replay pipelines. They help consumers reason about the relative freshness of writes for a key.
Do not design a distributed global clock aroundopIndex. Use it as ZoneTree intends: a producer freshness token for key-level conflict resolution.