SegmentIndex Architecture

This section describes the top-level index orchestration layer: how operations are routed, cached, and executed across segments.

Segment internals are intentionally centralized in Segment Architecture to avoid duplication.

SegmentIndex no longer uses the removed partition-overlay runtime. Writes are routed directly to stable segments, and read-after-write is provided by segment-local caches. Route-first split coordination remains a separate concern above stable segments.

Topics

• Read Path — request routing and lookup flow.
• Write Path — routed writes, flush, compaction, and split orchestration.
• WAL Runtime — internal ownership boundaries for WAL append, recovery, metadata, retention, and durability policy.
• Range-Partitioned Ingest — compatibility note describing what replaced the removed runtime model.
• Range-Partitioned Ingest Implementation Notes — current direct-to-segment write and route-split sequencing notes.
• Caching Strategy — index-level cache roles and sizing.
• Cache LRU — bounded LRU behavior and trade-offs.
• Performance Model & Sizing — throughput/latency model and tuning knobs.
• Metrics RouteMapSnapshot — stable index telemetry contract.
• Segment Index Concurrency — index thread-safety and lifecycle behavior, including OPENING, READY, CLOSING, CLOSED, and ERROR.
• Implementation — layer map from SegmentIndex down to Segment internals and where to inspect each responsibility.