feoxdb

Ultra-fast, embedded key-value database for Rust with sub-microsecond latency.

📚 Documentation | 📊 Benchmarks | 💬 Issues

Looking for a Redis-compatible server? Check out feox-server - a Redis protocol-compatible server built on Feox DB.

Features

• Sub-Microsecond Latency: <200ns GET, <700ns INSERT operations
• Lock-Free Concurrency: Built on SCC HashMap and Crossbeam SkipList
• io_uring Support (Linux): Kernel-bypass I/O for maximum throughput with minimal syscalls
• Flexible Storage: Memory-only or persistent modes with async I/O
• JSON Patch Support: RFC 6902 compliant partial updates for JSON values
• Atomic Operations: Compare-and-Swap (CAS) and atomic counters
• Write Buffering: Sharded buffers with batched writes to reduce contention
• CLOCK Cache: Second-chance eviction algorithm
• Statistics: Real-time performance monitoring
• Free Space Management: Dual RB-tree structure for O(log n) allocation
• Zero Fragmentation: Automatic coalescing prevents disk fragmentation

ACID Properties and Durability

FeOxDB provides ACI properties with relaxed durability:

• Atomicity: ✅ Individual operations are atomic via Arc-wrapped records
• Consistency: ✅ Timestamp-based conflict resolution ensures consistency
• Isolation: ✅ Lock-free reads and sharded writes provide operation isolation
• Durability: ⚠️ Write-behind logging with bounded data loss window

Durability Trade-offs

FeOxDB trades full durability for extreme performance:

• Write-behind buffering: Flushes every 100ms or when buffers fill (1024 entries or 16MB per shard)
• Worst-case data loss:
  • Time window: 100ms + 16MB / 4KB_random_write_QD1_throughput
  • Data at risk: 16MB × num_shards (num_shards = num_cpus / 2) (e.g., 64MB for 4 shards, 128MB for 8 shards)
  • Workers write in parallel, so time doesn't multiply with shards
  • Example (50MB/s 4KB random QD1): 420ms window, up to 64MB at risk (4 shards)
  • Example (200MB/s 4KB random QD1): 180ms window, up to 64MB at risk (4 shards)
• Memory-only mode: No durability, maximum performance
• Explicit flush: Call store.flush() to synchronously write all buffered data (blocks until fsync completes)

FAQ:

Q: Would the durability tradeoff for extreme performance worth it?

• For KV stores, there are more use cases that can accept this slightly relaxed durability model than not. of course this isn't the case for a main DB, but KV stores often handle derived data, caches, or state that can be rebuilt. That said, for cases needing stronger durability, you can call store.flush() after critical operations - gives you fsync-level guarantees. The philosophy is: make the fast path really fast for those who need it, but provide escape hatches for stronger guarantees when needed.

Q: What kind of applications would need this performance? Why these latency numbers matter?

• The real value isn't just raw speed - it's efficiency. When operations complete in 200ns instead of blocking for microseconds/milliseconds on fsync, you avoid thread pool exhaustion and connection queueing. Each sync operation blocks that thread until disk confirms - tying up memory, connection slots, and causing tail latency spikes.

  With FeOxDB's write-behind approach:

  • Operations return immediately, threads stay available
  • Background workers batch writes, amortizing sync costs across many operations
  • Same hardware can handle 100x more concurrent requests
  • Lower cloud bills from needing fewer instances

  For desktop apps, this means your KV store doesn't tie up threads that the UI needs. For servers, it means handling more users without scaling up. The durability tradeoff makes sense when you realize most KV workloads are derived data that can be rebuilt. Why block threads and exhaust IOPS for fsync-level durability on data that doesn't need it?

Quick Start

Installation

[dependencies]
feoxdb = "0.1.0"

Basic Usage

use feoxdb::FeoxStore;

fn main() -> feoxdb::Result<()> {
    // Create an in-memory store
    let store = FeoxStore::new(None)?;
    
    // Insert a key-value pair
    store.insert(b"user:123", b"{\"name\":\"Mehran\"}")?;
    
    // Get a value
    let value = store.get(b"user:123")?;
    println!("Value: {}", String::from_utf8_lossy(&value));
    
    // Check existence
    if store.contains_key(b"user:123") {
        println!("Key exists!");
    }
    
    // Delete a key
    store.delete(b"user:123")?;
    
    Ok(())
}

Persistent Storage

use feoxdb::FeoxStore;

fn main() -> feoxdb::Result<()> {
    // Create a persistent store
    let store = FeoxStore::new(Some("/path/to/data.feox".to_string()))?;
    
    // Operations are automatically persisted
    store.insert(b"config:app", b"production")?;
    
    // Flush to disk
    store.flush();
    
    // Data survives restarts
    drop(store);
    let store = FeoxStore::new(Some("/path/to/data.feox".to_string()))?;
    let value = store.get(b"config:app")?;
    assert_eq!(value, b"production");
    
    Ok(())
}

Advanced Configuration

use feoxdb::FeoxStore;

fn main() -> feoxdb::Result<()> {
    let store = FeoxStore::builder()
        .device_path("/data/myapp.feox")
        .file_size(10 * 1024 * 1024 * 1024)  // 10GB initial file size
        .max_memory(2_000_000_000)  // 2GB limit
        .enable_caching(true)        // Enable CLOCK cache
        .hash_bits(20)               // 1M hash buckets
        .enable_ttl(true)            // Enable TTL support
        .build()?;
    
    Ok(())
}

Time-To-Live (TTL) Support

use feoxdb::FeoxStore;

// Enable TTL feature via builder
let store = FeoxStore::builder()
    .enable_ttl(true)
    .build()?;

// Set key to expire after 60 seconds
store.insert_with_ttl(b"session:123", b"session_data", 60)?;

// Check remaining TTL
if let Some(ttl) = store.get_ttl(b"session:123")? {
    println!("Session expires in {} seconds", ttl);
}

// Extend TTL to 120 seconds
store.update_ttl(b"session:123", 120)?;

// Remove TTL (make permanent)
store.persist(b"session:123")?;

Concurrent Access

use feoxdb::FeoxStore;
use std::sync::Arc;
use std::thread;

fn main() -> feoxdb::Result<()> {
    let store = Arc::new(FeoxStore::new(None)?);
    let mut handles = vec![];
    
    // Spawn 10 threads, each inserting data
    for i in 0..10 {
        let store_clone = Arc::clone(&store);
        handles.push(thread::spawn(move || {
            for j in 0..1000 {
                let key = format!("thread_{}:key_{}", i, j);
                store_clone.insert(key.as_bytes(), b"value", None).unwrap();
            }
        }));
    }
    
    for handle in handles {
        handle.join().unwrap();
    }
    
    println!("Total keys: {}", store.len());  // 10,000
    Ok(())
}

Range Queries

use feoxdb::FeoxStore;

fn main() -> feoxdb::Result<()> {
    let store = FeoxStore::new(None)?;
    
    // Insert sorted keys
    store.insert(b"user:001", b"Mehran")?;
    store.insert(b"user:002", b"Bob")?;
    store.insert(b"user:003", b"Charlie")?;
    store.insert(b"user:004", b"David")?;
    
    // Range query: get users 001-003 (inclusive on both ends)
    let results = store.range_query(b"user:001", b"user:003", 10)?;
    
    for (key, value) in results {
        println!("{}: {}", 
            String::from_utf8_lossy(&key),
            String::from_utf8_lossy(&value));
    }
    // Outputs: user:001, user:002, user:003
    
    Ok(())
}

Compare-and-Swap (CAS) Operations

FeOxDB provides atomic Compare-and-Swap operations for implementing optimistic concurrency control:

use feoxdb::FeoxStore;
use std::sync::{Arc, Barrier};
use std::thread;

fn main() -> feoxdb::Result<()> {
    let store = Arc::new(FeoxStore::new(None)?);
    
    // Multiple servers processing orders concurrently
    
    store.insert(b"product:iPhone16:stock", b"50")?; // Initial stock
    let barrier = Arc::new(Barrier::new(5));
    let mut handles = vec![];
    
    for order_id in 0..5 {
        let store_clone = Arc::clone(&store);
        let barrier_clone = Arc::clone(&barrier);
        
        handles.push(thread::spawn(move || -> feoxdb::Result<bool> {
            barrier_clone.wait(); // Start all orders simultaneously
            
            let quantity_requested = 10;
            
            // Try to reserve inventory atomically
            let current = store_clone.get(b"product:iPhone16:stock")?;
            let stock: u32 = String::from_utf8_lossy(&current)
                .parse()
                .unwrap_or(0);
            
            if stock >= quantity_requested {
                let new_stock = (stock - quantity_requested).to_string();
                
                // Attempt atomic update
                if store_clone.compare_and_swap(
                    b"product:iPhone16:stock", 
                    &current, 
                    new_stock.as_bytes()
                )? {
                    return Ok(true); // Successfully reserved
                }
            }
            
            Ok(false) // Failed - insufficient stock or lost race
        }));
    }
    
    let successful_orders: Vec<bool> = handles
        .into_iter()
        .map(|h| h.join().unwrap().unwrap())
        .collect();
    
    // With single-attempt CAS, some orders may fail due to races
    // Typically 3-4 orders succeed out of 5
    let successful_count = successful_orders.iter().filter(|&&x| x).count();
    println!("Successful orders: {}/5", successful_count);
    
    let final_stock = store.get(b"product:iPhone16:stock")?;
    println!("Final stock: {}", String::from_utf8_lossy(&final_stock));
    
    Ok(())
}

CAS operations enable:

• Optimistic concurrency control - Update only if value hasn't changed
• Lock-free updates - No mutexes or blocking required
• Atomic state transitions - Safely move between states without races
• Fast conflict detection - Immediate failure when values don't match

JSON Patch Operations (RFC 6902)

FeOxDB supports partial updates to JSON documents using the standard JSON Patch format:

use feoxdb::FeoxStore;

fn main() -> feoxdb::Result<()> {
    let store = FeoxStore::new(None)?;
    
    // Store a JSON document
    let user = r#"{
        "name": "Mehran",
        "age": 30,
        "skills": ["Rust", "Go"],
        "address": {
            "city": "San Francisco",
            "zip": "94105"
        }
    }"#;
    store.insert(b"user:123", user.as_bytes())?;
    
    // Apply patches to modify specific fields
    let patches = r#"[
        {"op": "replace", "path": "/age", "value": 31},
        {"op": "add", "path": "/skills/-", "value": "Python"},
        {"op": "add", "path": "/email", "value": "mehran@example.com"},
        {"op": "replace", "path": "/address/city", "value": "Seattle"}
    ]"#;
    
    store.json_patch(b"user:123", patches.as_bytes())?;
    
    // Document is now updated with patches applied
    let updated = store.get(b"user:123")?;
    println!("Updated: {}", String::from_utf8_lossy(&updated));
    
    Ok(())
}

Supported JSON Patch operations:

• add: Add a new field or array element
• remove: Remove a field or array element
• replace: Replace an existing value
• move: Move a value from one path to another
• copy: Copy a value from one path to another
• test: Test that a value at a path equals a specified value

Atomic Counter Operations

use feoxdb::FeoxStore;

fn main() -> feoxdb::Result<()> {
    let store = FeoxStore::new(None)?;
    
    // Initialize counters (must be 8-byte i64 values)
    let zero: i64 = 0;
    store.insert(b"stats:visits", &zero.to_le_bytes())?;
    store.insert(b"stats:downloads", &zero.to_le_bytes())?;
    
    // Increment atomically (thread-safe)
    let visits = store.atomic_increment(b"stats:visits", 1)?;
    println!("Visits: {}", visits);  // 1
    
    // Increment by 10
    let downloads = store.atomic_increment(b"stats:downloads", 10)?;
    println!("Downloads: {}", downloads);  // 10
    
    // Decrement
    let visits = store.atomic_increment(b"stats:visits", -1)?;
    println!("Visits after decrement: {}", visits);  // 0
    
    Ok(())
}

Performance

Benchmarks

Run the included benchmarks:

# Deterministic test
cargo run --release --example deterministic_test 100000 100

# Criterion benchmarks
cargo bench

Results

Typical performance on M3 Max:

Throughput

Based on Criterion benchmarks with SCC HashMap:

• GET: 11-14M ops/sec (varies by batch size)
• INSERT: 1.0-1.8M ops/sec (varies by batch size)
• DELETE: ~4M ops/sec
• Mixed workload (80/20): 3.8M ops/sec

Architecture

FeOxDB uses a lock-free, multi-tier architecture optimized for modern multi-core CPUs:

Lock-Free Design

The entire hot path is lock-free, ensuring consistent sub-microsecond latency:

• SCC HashMap: Fine-grained locking hash table optimized for highly concurrent workloads
• Crossbeam SkipList: Fully lock-free ordered index for range queries
• Atomic Operations: All metadata updates use atomic primitives
• RCU-style Access: Read-Copy-Update pattern for zero-cost reads

Async Write-Behind Logging

Writes are decoupled from disk I/O for maximum throughput:

1. Sharded Write Buffers

   • Multiple buffers with thread-consistent assignment
   • Reduces contention between threads
   • Cache-friendly access patterns

2. Batched Flushing

   • Writes accumulated and flushed in batches
   • Optimal disk utilization with large sequential writes
   • Configurable flush intervals

3. io_uring Integration (Linux)

   • Kernel-bypass I/O with submission/completion queues
   • Zero-copy operations where possible
   • Async I/O without thread pool overhead

4. Write Coalescing

   • Multiple updates to same key automatically merged
   • Reduces write amplification
   • Improves SSD lifespan

Storage Tiers

1. In-Memory Layer

   • Primary storage in SCC HashMap
   • O(1) lookups with ~100ns latency
   • Automatic memory management

2. Write Buffer Layer

   • Sharded buffers for concurrent writes
   • Lock-free MPSC queues
   • Backpressure handling

3. Persistent Storage

   • Sector-aligned writes (4KB blocks)
   • Write-ahead logging for durability
   • Crash recovery support

4. Cache Layer

   • CLOCK eviction algorithm
   • Keeps hot data in memory after disk write
   • Transparent cache management

Build Configuration

Memory Allocator

FeOxDB uses jemalloc by default for better performance, especially in multi-threaded workloads.

To opt-out of jemalloc and use the system allocator instead:

# Build with system allocator
cargo build --no-default-features --features system-alloc

# Install with system allocator
cargo install feoxdb --no-default-features --features system-alloc

Use the system allocator when:

• Building for embedded systems with tight memory constraints
• Debugging with memory profiling tools (valgrind, AddressSanitizer)
• Targeting platforms where jemalloc doesn't compile (some musl targets)
• You need the smallest possible binary size (saves ~200-300KB)

API Documentation

Full API documentation is available:

cargo doc --open

Key types:

• FeoxStore - Main database interface
• StoreBuilder - Configuration builder
• FeoxError - Error types
• Statistics - Performance metrics

Examples

See the examples/ directory for more:

• basic_usage.rs - Basic usage example
• cas_example.rs - Compare-and-swap (CAS) example
• deterministic_test.rs - Reproducible performance test

Contributing

Contributions are welcome! See CONTRIBUTING.md for more information.

License

Copyright 2025 Mehran Toosi

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

See LICENSE for the full license text.