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openraft-fjall-kv-example

A fjall-backed persistent storage implementation for Openraft, demonstrating production-ready log storage and state machine patterns.

Key Features Demonstrated

Persistent storage: [RaftLogStorage] and [RaftStateMachine] with fjall
Column families: Separate storage for logs, state machine, and metadata
Durability: On-disk persistence for cluster recovery
Performance: Efficient batch operations and compaction

Overview

This example implements:

RaftLogStorage - Persistent Raft log storage
RaftStateMachine - Persistent application state machine

Built with fjall v3 for production-grade durability and performance.

Architecture

Storage structure:

Logs stored in dedicated fjall key space
State machine data in separate key space
Vote and metadata persisted independently

Asynchronous I/O operations:

WAL flush operations run in spawned tasks to avoid blocking the async runtime
save_vote() and append_to_log() spawn async tasks for disk persistence
Callbacks receive actual flush results for proper error propagation
Log truncation (purge()) doesn't require immediate persistence

Key Code Locations:

Storage implementation: src/store.rs
Log storage with async WAL flush: src/log_store.rs
Type definitions: See parent example for network and client implementations

Comparison

Feature	kv-fjall	memstore
Storage	fjall (disk)	Memory
Persistence	Yes	No
Recovery	Full	None
Complexity	Higher	Lower

Built for testing and demonstration purposes.