Architecture

Astra combines strict CP semantics with low-latency write handling under constrained disks.

Canonical, actively maintained architecture docs:

High-Level Design

flowchart LR C[etcd gRPC clients] --> K[KV/Watch Frontend] K --> R[OpenRaft Replication] R --> S[In-memory MVCC + Watch Ring] R --> W[Unified WAL / Log Store] S --> L[Compaction + LSM key/meta] L --> O[S3/MinIO cold SST tier]

Why Astra Outperforms etcd in Target Scenarios

Unified WAL with vectorized append and bounded linger.
Queue-aware adaptive batching and byte-budgeted put packing.
Semantic QoS lane for lease/lock prefixes under pressure.
Read isolation and list prefetch controls to prevent write storms from collapsing read latency.
Object-tiered compacted state with manifest-driven restore.

Zero-Copy Watch Ring

Watch events are published from memory ring buffers instead of replaying from disk scans. This keeps high fanout watch workloads detached from storage jitter.

Semantic QoS

Tier-0 keys (for example lease/lock lanes) are classified and routed through a priority queue. When normal lane pressure increases, Tier-0 writes bypass the stall path to protect control-plane liveness.

Raft Stage Timeline

Astra emits timeline telemetry for enqueue, append, replication, quorum-ack, and apply stages. These traces enable targeted tuning by identifying true idle gaps versus disk-bound stalls.