Redis Clone in C

A Redis-compatible server implementation in C, supporting basic RESP protocol commands.

Features

• ✅ PING/PONG - Basic connectivity test
• ✅ SET - Store key-value pairs
• ✅ GET - Retrieve values by key
• ✅ Multi-threaded - Handles multiple concurrent clients
• ✅ RESP Protocol - Full RESP encoding/decoding support
• ✅ Thread-safe - Hash map with mutex protection

Project Structure

redis-c/
├── src/
│   ├── main.c          # Server main loop and command handling
│   ├── decode.c        # RESP protocol decoder
│   ├── encode.c        # RESP protocol encoder
│   ├── hash_map.c      # Thread-safe hash map implementation
│   ├── resp.h          # RESP types and declarations
│   └── hash_map.h      # Hash map declarations
├── CMakeLists.txt      # CMake build configuration
└── run_server.sh       # Helper script to run server

Prerequisites

• CMake (version 3.13 or higher)
• GCC or compatible C compiler (C11 standard)
• redis-cli for testing

Install on Ubuntu/Debian:

sudo apt-get install cmake build-essential redis-tools

Building

# Clone or navigate to project directory
cd redis-c

# Build the project
mkdir -p build
cd build
cmake ..
make
cd ..

The executable will be created at build/redis.

Running the Server

Method 1: Using the helper script

./run_server.sh

Method 2: Direct execution

./build/redis

The server will start and listen on port 6379. You'll see:

Redis server starting...
Server listening on port 6379
Ready to accept connections.

Press Ctrl+C to stop the server.

Testing the Server

Using redis-cli (Interactive Testing)

Use redis-cli to test the server. It's the official Redis command-line interface and handles RESP protocol automatically.

Installation

# Ubuntu/Debian
sudo apt-get install redis-tools

# macOS
brew install redis

Basic Usage

Terminal 1 - Start the server:

./run_server.sh

Terminal 2 - Connect with redis-cli:

redis-cli -p 6379

Commands in redis-cli

Once connected, you can use normal Redis commands:

127.0.0.1:6379> PING
PONG

127.0.0.1:6379> SET mykey "Hello World"
OK

127.0.0.1:6379> GET mykey
"Hello World"

127.0.0.1:6379> GET nonexist
(nil)

127.0.0.1:6379> SET foo bar
OK

127.0.0.1:6379> GET foo
"bar"

127.0.0.1:6379> EXIT

One-line Commands

You can also run commands directly without entering interactive mode:

redis-cli -p 6379 PING
# Output: PONG

redis-cli -p 6379 SET mykey "Hello"
# Output: OK

redis-cli -p 6379 GET mykey
# Output: "Hello"

---

Performance Benchmarking

Using redis-benchmark (Recommended)

redis-benchmark is the official Redis performance testing tool. It's much faster and more accurate than custom scripts.

Installation

# Ubuntu/Debian
sudo apt-get install redis-tools

# macOS
brew install redis

Quick Benchmark

Terminal 1 - Start the server:

./run_server.sh

Terminal 2 - Run benchmark:

# 1 million SET operations with 50 concurrent clients
redis-benchmark -h localhost -p 6379 -t set -n 1000000 -c 50

# 1 million GET operations
redis-benchmark -h localhost -p 6379 -t get -n 1000000 -c 50

# PING test
redis-benchmark -h localhost -p 6379 -t ping -n 100000 -c 50

Using the Benchmark Script

We provide a convenient wrapper script:

# Default: 1M SET requests with 50 clients
./tests/redis-benchmark.sh

# Custom options
./tests/redis-benchmark.sh -n 1000000 -c 50 -t set
./tests/redis-benchmark.sh -n 100000 -c 10 -t get

# Run all tests (PING, SET, GET)
./tests/redis-benchmark.sh --all

# See all options
./tests/redis-benchmark.sh --help

Benchmark Output Example

====== SET ======
  1000000 requests completed in 45.23 seconds
  50 parallel clients
  3 bytes payload
  keep alive: 1
  host configuration "save": 
  host configuration "appendonly": no
  multi-thread: no

0.00% <= 1 milliseconds
95.50% <= 2 milliseconds
99.90% <= 3 milliseconds
100.00% <= 4 milliseconds

22105.12 requests per second

Common Benchmark Commands

Command	Description
redis-benchmark -h localhost -p 6379 -t set -n 1000000 -c 50	1M SET operations, 50 clients
redis-benchmark -h localhost -p 6379 -t get -n 1000000 -c 50	1M GET operations, 50 clients
redis-benchmark -h localhost -p 6379 -t ping -n 100000 -c 50	100K PING operations
redis-benchmark -h localhost -p 6379 -t set,get -n 100000 -c 10	Mixed SET/GET test

---

RESP Protocol Format

Commands are sent in RESP (Redis Serialization Protocol) format:

• *N - Array with N elements
• $N - Bulk string of length N
• +text - Simple string
• -text - Error
• :number - Integer

Example: SET Command

The command SET mykey "Hello World" in RESP format:

*3          ← Array with 3 elements
$3          ← Bulk string of length 3
SET         ← Command name
$5          ← Bulk string of length 5
mykey       ← Key
$11         ← Bulk string of length 11
Hello World ← Value

Note: You don't need to know RESP format when using redis-cli - it handles this automatically!

---

Implementation Details

Architecture

• Multi-threaded server using pthread for concurrent client handling
• Thread-safe hash map with mutex protection for GET/SET operations
• RESP parser with proper error handling and bounds checking
• Memory management with proper cleanup of all allocated resources

Commands Supported

Command	Description	redis-cli Example
PING	Returns PONG	PING
SET key value	Store key-value pair	SET foo bar
GET key	Retrieve value by key	GET foo

Error Handling

• Invalid commands return error responses
• Incomplete messages are buffered until complete
• Protocol errors are handled gracefully

---

Development

Building for Development

cd build
cmake -DCMAKE_BUILD_TYPE=Debug ..
make

Code Structure

• main.c - Server socket handling, command processing
• decode.c - RESP parsing from network bytes
• encode.c - RESP encoding to network bytes
• hash_map.c - Dictionary/hash table implementation

---

Troubleshooting

Port already in use

# Find and kill existing process
lsof -ti:6379 | xargs kill -9
# Or
pkill -f redis

Connection refused

• Make sure the server is running in another terminal
• Check that port 6379 is not blocked by firewall
• Verify server started successfully (check for "Server listening" message)

redis-cli not found

# Install redis-tools
sudo apt-get install redis-tools  # Ubuntu/Debian
brew install redis                # macOS

Commands not working

• Check server logs for error messages
• Make sure you're using correct Redis command syntax
• Verify the server is running and listening on port 6379

---

Files Reference

Required Files

• .codecrafters/ - Keep if submitting to CodeCrafters platform, otherwise not needed
• your_program.sh - Keep if submitting to CodeCrafters platform, otherwise not needed
• CMakeLists.txt - Required for building
• src/ - Source code (required)

Optional Files

• run_server.sh - Helper script (optional, but recommended)
• tests/redis-benchmark.sh - Benchmark script using redis-benchmark (recommended)
• tests/stress-test.sh - Custom stress test script (alternative)
• build/ - Build directory (auto-generated, can be deleted)

---

Quick Start Summary

1. Build:

   mkdir -p build && cd build && cmake .. && make && cd ..

2. Run server:

   ./run_server.sh

3. Test:

   redis-cli -p 6379

   Then type commands like PING, SET foo bar, GET foo

---

License

This project is part of the CodeCrafters Redis challenge.