dblite

A lightweight, embeddable key-value store inspired by SQLite. Simple, fast, and built for embedding into your Rust applications or using as a standalone CLI tool.

Features

• Simple Key-Value Storage: Store and retrieve arbitrary data by string keys
• File-Based Persistence: All data stored in a single file on disk
• ACID Guarantees: File-level locking ensures data integrity
• TTL Support: Set expiration times on keys
• Space Reuse: Deleted records' space is automatically reused for new data
• Compaction: Reclaim disk space by removing deleted/expired records
• Embeddable Library: Use as a Rust library in your projects
• Interactive CLI: REPL interface with command completion

Installation

From Source

git clone https://github.com/yourusername/dblite.git
cd dblite
cargo build --release

The binary will be available at target/release/dblite

Install Globally

cargo install --path .

Usage

CLI Tool

Starting the REPL

dblite /path/to/database.db

This opens an interactive shell where you can execute commands.

Available Commands

SET - Store a key-value pair

dblite> SET mykey "Hello, World!"
OK

dblite> SET user:123 '{"name":"Alice","age":30}'
OK

SET with TTL - Store a key with expiration time

dblite> SET session:abc token123 30s
OK

dblite> SET cache:data value 5m
OK

TTL formats: 30s (seconds), 5m (minutes), 2h (hours), 1d (days)

GET - Retrieve a value

dblite> GET mykey
Hello, World!

dblite> GET nonexistent
(nil)

DEL - Delete a key

dblite> DEL mykey
1

dblite> DEL nonexistent
0

COMPACT - Reclaim disk space

dblite> COMPACT
OK

Removes deleted records and optimizes file size.

EXIT or QUIT - Close the CLI

dblite> EXIT
bye

As a Rust Library

Add to your Cargo.toml:

[dependencies]
dblite = "0.1"

For minimal binary size (excludes CLI command parser):

[dependencies]
dblite = { version = "0.1", default-features = false }

This reduces the library from ~300KB to ~260KB by removing the CLI module and its dependencies (rustyline, humantime).

Basic Usage

use dblite::{Database, LockMode};
use std::time::Duration;

fn main() -> std::io::Result<()> {
    // Open or create a database
    let mut db = Database::open_or_create("~/mydb.dbl")?;
    
    // Store a value
    db.set("username", b"alice")?;
    
    // Store with TTL (expires in 60 seconds)
    db.set_with_ttl("session_token", b"abc123", Duration::from_secs(60))?;
    
    // Retrieve a value
    if let Some(value) = db.get("username")? {
        println!("Username: {}", String::from_utf8_lossy(&value));
    }
    
    // Check if key exists
    if db.contains_key("username")? {
        println!("User exists!");
    }
    
    // Delete a key
    let deleted = db.delete("username")?;
    println!("Deleted: {}", deleted);
    
    // Get all keys
    let keys = db.keys()?;
    println!("Keys: {:?}", keys);
    
    // Compact the database
    db.compact()?;
    
    Ok(())
}

Advanced: Using the Store Directly

use dblite::{KeyValueStore, LockMode};
use std::time::Duration;

fn main() -> std::io::Result<()> {
    // Open with exclusive lock
    let mut store = KeyValueStore::open("data.db", LockMode::Exclusive)?;
    
    // Store data
    store.put("key", b"value")?;
    
    // Store with TTL
    store.put_with_ttl("temp", b"data", Some(Duration::from_secs(300)))?;
    
    // Retrieve
    if let Some(data) = store.get("key")? {
        println!("Got: {:?}", data);
    }
    
    // Remove
    store.remove("key")?;
    
    Ok(())
}

Read-Only Access

use dblite::{KeyValueStore, LockMode};

fn main() -> std::io::Result<()> {
    // Open in shared mode (read-only)
    let mut store = KeyValueStore::open("data.db", LockMode::Shared)?;
    
    // Read operations work
    let value = store.get("key")?;
    
    // Write operations will fail with PermissionDenied
    // store.put("key", b"value")?; // Error!
    
    Ok(())
}

File Format

dblite stores data in a single file with the following structure:

• Header: Magic bytes (DBL1) + version number
• Records: Sequence of key-value records with metadata
  • Record type (insert/delete)
  • Key length and data
  • Value length and data
  • Capacity (for space reuse)
  • Optional expiration timestamp

The file format is designed for:

• Efficiency: Records are aligned for fast access
• Durability: All writes are flushed to disk
• Space Reuse: Deleted space is tracked and reused
• Simplicity: Single-file storage like SQLite

Architecture

Key Components

• KeyValueStore: Low-level storage engine with file I/O and indexing
• Database: High-level API wrapping the store
• InMemoryIndex: BTreeMap-based index for fast key lookups
• FreeSpaceManager: Tracks and reuses deleted record space
• FileLock: OS-level file locking for concurrent access control

Concurrency Model

• Exclusive Lock: One writer, no readers (LockMode::Exclusive)
• Shared Lock: Multiple readers, no writers (LockMode::Shared)
• OS-level file locking prevents data corruption
• Index is rebuilt from file on open

Performance Characteristics

• Reads: O(log n) via in-memory BTreeMap index
• Writes: O(log n) index update + O(1) append or O(n) space reuse scan
• Deletes: O(log n) index update + O(1) free space tracking
• Compaction: O(n) full file rewrite
• Memory: O(n) for key index (keys + metadata only, not values)

Limitations

• Single-file: All data in one file (simple but not distributed)
• In-memory index: Keys must fit in memory
• No transactions: Individual operations are atomic, but no multi-key transactions
• No query language: Simple get/set/delete operations only
• File-level locking: Not optimized for high-concurrency scenarios

Building

Development Build

cargo build

Release Build

cargo build --release

Running Tests

cargo test

License

This project is licensed under the MIT License.

See the LICENSE file for details.

Project Status

This is a hobby project created over a holiday. It's functional and tested, but not battle-tested in production environments. Please contact me know if you would like to battle test it :3