CrimsonCache

CrimsonCache is a custom in-memory data store inspired by Redis, offering essential caching commands, data persistence, and replication. It's built as a robust learning tool for exploring networking, concurrency, and distributed systems.

Features

• Core Functionality

  • In-memory key-value storage with efficient hash table implementation
  • Support for string data type (with more planned)
  • Key expiration mechanism with TTL
  • LRU cache eviction for memory management

• Networking

  • TCP server with IPv4/IPv6 dual-stack support
  • RESP (Redis Serialization Protocol) compatible responses
  • Support for 50+ concurrent client connections via multi-threading
  • Clean connection handling and error management

• Persistence

  • RDB-style snapshot persistence for point-in-time recovery
  • Background saving with fork() for non-blocking operation
  • Automatic periodic saving based on changes and time
  • Atomic file operations for crash-safe persistence

• Planned Features

  • Primary-replica replication
  • Additional data types (lists, sets)
  • Transaction support (MULTI/EXEC)
  • Pub/Sub messaging system
  • Basic authentication

Getting Started

Prerequisites

• GCC/Clang compiler
• Make build system
• POSIX-compliant OS (Linux, macOS, etc.)

Installation

git clone https://github.com/yourusername/CrimsonCache.git
cd CrimsonCache
make

Usage

./bin/crimsoncache

Connect to Running Server

Method 1: Using Netcat (nc)

Open a new terminal window and use netcat to connect to your server:

nc localhost 6379

Once connected, type PING and press Enter. You should see:

PING
+PONG

Method 2: Using Telnet

telnet localhost 6379

Once connected, type PING and press Enter. You should see:

PING
+PONG

Method 3: Using Redis CLI (if installed)

If you happen to have the Redis command line interface installed:

redis-cli -p 6379 ping

This should return PONG.

Supported Commands

CrimsonCache currently supports the following commands:

Basic Commands

• PING [message] - Test connectivity, returns PONG or the message if provided
• SET key value [EX seconds] - Set a key to a value with optional expiration
• GET key - Get the value of a key
• DEL key [key ...] - Delete one or more keys
• EXISTS key [key ...] - Check if keys exist
• EXPIRE key seconds - Set a key's time to live in seconds
• TTL key - Get the time to live for a key

Persistence Operations

• SAVE - Synchronously save the dataset to disk
• BGSAVE - Asynchronously save the dataset to disk in the background

Data Persistence

CrimsonCache provides RDB-style persistence similar to Redis:

• Automatic Saving: The database is automatically saved to disk:

  • After a specified number of changes (default: 1000)
  • After a specified time period (default: 300 seconds/5 minutes)

• Manual Saving: You can trigger persistence manually:

  • SAVE command performs a blocking save operation
  • BGSAVE command saves in the background without blocking

• Recovery: When the server starts, it automatically loads the latest snapshot from disk.

Testing Your Redis-compatible Commands

Since CrimsonCache implements Redis protocol, you can use any Redis client to interact with it:

# Using redis-cli
redis-cli -p 6379 set mykey "Hello World"
redis-cli -p 6379 get mykey

# Using netcat
nc localhost 6379
SET mykey "Hello World"
GET mykey

Implementation Details

• Multi-threaded architecture for handling client connections
• Dual-stack IPv4/IPv6 networking implementation
• LRU cache eviction algorithm for memory management
• Fork-based background saving for non-blocking persistence
• Properly handles quoted strings in commands

License

MIT License - See LICENSE file for details.