Caching in Web Applications: Explained with Simple Examples

Caching is the process of storing frequently used data in memory.
An example of this is when a teacher asks a student, “What is the capital of China?”
The student searches for the answer in a book and replies.
The next time the teacher asks the same question, the student answers quickly—without needing to look it up again.
Similarly, caching works this way: when a resource is requested, if it’s not already present in memory, it is fetched from the original source and stored in cache memory.
The next time that same resource is requested, it is served directly from the cache.

In a web application, caching happens at different levels:

• Browser: The browser caches static data such as images, CSS, and JavaScript files.
• Proxy: A proxy server acts as an intermediary between the client and the original server. It caches data to allow users quicker access to resources.
• Server: The server can cache HTML content of commonly accessed pages. It can also cache the results of SQL queries.

Controlling Caching with HTTP Headers:

We can control caching behavior by using proper HTTP headers, which tell the browser what to cache and for how long.
Some common headers include:

• max-age: Defines the time (in seconds) before the cached copy expires.
• no-cache: The browser can cache the response but must first submit a validation request to the origin server.
• no-store: Browsers are not allowed to cache the response at all.
• public: The resource can be cached by any cache (browser, proxy, etc.).
• private: The response can only be cached on the client’s device.

These headers must be set by the server.
On Apache servers, you can set them in the .htaccess file using the mod_headers and mod_expires directives.

Third-Party Caching Solutions:

Most websites today use third-party caching solutions like Memcached, Nginx, and Redis to boost server performance.

• Memcached is an open-source, distributed caching system.
  It uses a key-value pair model to store data in memory and is best suited for data-driven applications.
  If you have a query that is used repeatedly and returns the same result, it can be cached in Memcached.
  Future requests for the same data will be served from the cache, reducing database trips—especially helpful when many users request the same data at once.
• Memcached is ideal for storing small data.
  If you need to cache larger or more complex data, Redis is a better choice.
• Redis can also function as a database and supports advanced data types like strings, hashes, lists, and sets.
  It even allows you to perform operations on cached data, giving it more flexibility than Memcached.

Best Practices for Caching:

When using caching, it’s important to note:

• Not all data should be cached, especially data that changes frequently.
• Caching outdated data can lead to user confusion or incorrect information.
• You must carefully decide what data to cache and how long to cache it.

Summary:

Caching is a powerful technique to speed up web performance, reduce server load, and improve user experience—but it must be used wisely.

Ricky Noronha