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Memcached: Distributed Memory Object Caching

Memcached is a high-performance, distributed memory object caching system, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load. It's an in-memory key-value store for small arbitrary data (strings, objects) resulting from database calls, API calls, or page rendering.

Key Features​

  • Simple Key-Value Store: Memcached stores data as key-value pairs in RAM, providing fast access.
  • Distributed Architecture: Memcached can be deployed across multiple servers, creating a distributed cache. This allows for scaling to handle large amounts of data and high traffic.
  • In-Memory Caching: All data is stored in memory, providing very low latency access times.
  • Speed and Efficiency: Designed for speed and efficiency, minimizing overhead and maximizing throughput.
  • Client Libraries: Numerous client libraries are available for various programming languages (e.g., PHP, Python, Java, C/C++, .NET).
  • LRU (Least Recently Used) Eviction: When memory is full, Memcached evicts the least recently used items to make room for new data.
  • Simple Protocol: Uses a plain text protocol, making it easy to understand and implement.
  • Multi-Threaded: Can utilize multiple CPU cores for improved performance (depending on the implementation).

Use Cases​

  • Database Caching: Cache the results of database queries to reduce database load and improve application performance.
  • Session Caching: Store user session data in memory for faster access.
  • API Response Caching: Cache API responses to reduce the load on backend services.
  • Object Caching: Cache frequently accessed objects in memory.
  • Page Fragment Caching - Store parts of a web page such as navigation bars or product listings
  • Image Caching: Cache frequently accessed images to speed up page load times.
  • Content Delivery Network (CDN) Support: Memcached can be used as a caching layer in CDNs.

Getting Started​

  1. Installation: Install Memcached on your server(s). The installation process varies depending on your operating system.

    • Linux (Debian/Ubuntu): sudo apt-get install memcached
    • Linux (CentOS/RHEL): sudo yum install memcached
    • macOS (using Homebrew): brew install memcached

  2. Configuration: Configure Memcached settings, such as memory allocation, port, and listening address. The configuration file is typically located at /etc/memcached.conf or /etc/sysconfig/memcached.

  3. Client Library: Use a Memcached client library in your application code to interact with the Memcached server(s).

Example (Python with python-memcached):​

import memcache

mc = memcache.Client(['127.0.0.1:11211'], debug=0)  # Connect to Memcached server

mc.set('my_key', 'my_value')  # Store a value

value = mc.get('my_key')  # Retrieve the value

print(value)  # Output: my_value

Configuration Options​

Key configuration options found in memcached.conf or similar:

  • -m <megabytes>: Specifies the maximum amount of memory to use (in MB).
  • -p <port>: Specifies the port number to listen on (default: 11211).
  • -l <address>: Specifies the IP address to listen on (default: INADDR_ANY, meaning all interfaces). Use -l 127.0.0.1 for local access only.
  • -u <user>: Run the daemon as username.
  • -c <connections>: Specifies the maximum number of concurrent connections (default: 1024).
  • -d: Run as a daemon.

Considerations​

  • Memory Management: Properly configure the -m option to allocate sufficient memory for your caching needs. Monitor memory usage to avoid eviction thrashing.
  • Eviction Policy: Memcached uses LRU (Least Recently Used) eviction. Consider the implications of this policy for your data.
  • Network Configuration: Ensure that your network is properly configured to allow clients to connect to the Memcached server(s).
  • Security: If exposing Memcached to a public network, implement appropriate security measures (e.g., firewall rules, authentication - SASL support available).

Monitoring​

Monitor Memcached performance using command-line tools like telnet or dedicated monitoring solutions. The stats command provides useful information about server performance, memory usage, and cache hit rates.

telnet localhost 11211
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
stats
... (output) ...
quit

Limitations​

  • Limited Data Types: Only supports storing strings and serialized objects.
  • No Persistence: Data is lost when the server is restarted. If persistence is needed, consider using Redis.
  • Security: Memcached generally lacks strong security features by default, requiring additional configuration or a network secured from unauthorized traffic. SASL authentication is supported.

Resources​

This documentation provides a solid basis for using Memcached. Make sure to update the example code and monitoring sections to match your specific environment. Good luck!