vkdb

A lightweight, high-performance key-value store with notification capabilities, written in Java.

Overview

vkdb is an in-memory key-value database server inspired by Redis. It demonstrates concurrent programming, networking, and event notification patterns in Java. Built using modern Java features like virtual threads, vkdb provides a simple yet powerful database for learning and experimentation.

Key Features

• ✓ In-memory Key-Value Storage: Fast data operations with O(1) average time complexity
• ✓ Concurrent Client Connections: Handles multiple clients simultaneously with Java's virtual threads
• ✓ Real-time Notifications: Subscribe to key changes with the NOTIFY command
• ✓ Simple Text Protocol: Easy-to-use command interface similar to Redis
• ✓ Scalable Architecture: Designed to handle thousands of concurrent connections
• ✓ Logging System: Comprehensive logging for debugging and monitoring

Quick Start

Prerequisites

• Java 21 or higher (for virtual threads support)
• Maven

Installation

# Clone the repository
git clone https://github.com/vmskonakanchi/vkdb.git
cd vkdb

# Build the project
mvn clean package

Running the Server

java -jar server/target/vkdb-1.0.jar

Running the Client

java -jar client/target/vkdb-client-1.0.jar

Usage Examples

Basic Operations

vkdb> SET user1 "John Doe"
SAVED
vkdb> SETX user1 "John Doe" 10000 # set key with with expiry
SAVED
vkdb> GET user1
John Doe
vkdb> DEL user1
DELETED

Notification System

In Client 1

vkdb> NOTIFY user1
OK

In Client 2

vkdb> SET user1 "Jane Smith"

Client 1 will automatically receive:

CHANGED user1 Jane Smith

Command Reference

Command	Format	Description
SET	SET <KEY> <VALUE>	Sets a key to hold the specified value
SETX	SETX <KEY> <VALUE> <TTL>	Sets a key to hold the specified value with expiry time in milliseconds
GET	GET <KEY>	Gets the value of a key
DEL	DEL <KEY>	Deletes a key
BEGIN	BEGIN	Begins a transaction
COMMIT	COMMIT	Commit a transaction
REGISTER	REGISTER <USERNAME> <PASSWORD>	Register a user with username and password
LOGIN	LOGIN <USERNAME> <PASSWORD>	Login a user with username and password
WHOAMI	WHOAMI	Gets the current logged in user
NOTIFY	NOTIFY <KEY>	Subscribe to changes for a specific key
DISCONNECT	DISCONNECT	Closes the connection to the server

Project Roadmap

• Persistence: Save/restore data from disk
• Key Expiration: Set time-to-live for keys
• Command Pipelining: Batch multiple commands
• Authentication: Simple password protection
• Admin Dashboard: Web interface for monitoring and management
• Clustering: Distributed operation across multiple nodes
• Data Types: Support for lists, sets, and hashes

Architecture

vkdb uses a client-server architecture with the following components:

• Server: Central component that accepts client connections
• ClientHandler: Manages individual client sessions and commands
• NotifyItem: Handles the notification system for key changes
• SocketItem: Encapsulates socket communication details
• SaveItem: Encapsulates data storage and expiration
• AuthUser: Encapsulates user storage and retrival and other logic

The notification system is implemented using a publisher-subscriber pattern with a non-blocking queue for processing notifications asynchronously.

Contributing

Contributions are welcome! Here are ways you can contribute:

• Implement / Suggest new features from the roadmap
• Improve performance or memory efficiency
• Add tests and documentation
• Report bugs and suggest enhancements

Please see CONTRIBUTING.md for more details.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Acknowledgements

• Inspired by Redis
• Built with Java virtual threads (Project Loom)