Memcached vs Varnish: What are the differences?

Introduction

In this article, we will discuss the key differences between Memcached and Varnish, two popular caching systems used in website optimization.

1. Scalability: Memcached is a distributed caching system that allows for horizontal scalability by adding more servers to the cache pool. It uses a hash-based algorithm for storing and retrieving data, making it suitable for large-scale applications. On the other hand, Varnish is a reverse proxy cache that can handle high traffic loads and improve website performance by caching static content. It is designed to be deployed in front of web servers and can be scaled vertically by increasing hardware resources.

2. Caching Mechanism: Memcached is a key-value cache that stores data in memory, enabling fast data retrieval. It is commonly used to cache database query results, API responses, and other frequently accessed data. Varnish, on the other hand, caches entire HTTP responses, including HTML pages, images, and CSS files. It uses an advanced caching mechanism that takes into account headers and cookies to determine if a resource can be served from cache or needs to be retrieved from the backend.

3. Purging and Invalidation: Memcached does not provide built-in mechanisms for purging or invalidating cached data. To remove data from the cache, the application needs to explicitly overwrite or delete the corresponding key-value pair. In contrast, Varnish allows for granular control over cache invalidation. It provides a flexible configuration language that enables cache purging based on different criteria such as URL, HTTP method, or response headers. This makes Varnish more suitable for dynamic websites that frequently update their content.

4. Content Delivery Network (CDN) Support: Memcached does not have native support for CDN integration. It primarily focuses on caching data within a distributed cluster of servers. Varnish, on the other hand, can be used as a front-end cache for a CDN. It can sit between the CDN edge servers and the origin servers, caching frequently accessed content at the edge locations and reducing the load on the backend infrastructure.

5. Request Processing: Memcached operates at the transport layer (Layer 4) of the OSI model and does not parse or modify the content of the requests or responses. It simply stores and retrieves data based on the provided key. Varnish, on the other hand, functions at the application layer (Layer 7) and provides advanced features like request rewriting, header manipulation, and load balancing. It can be configured to modify request and response headers, route traffic to different backend servers, and perform other custom actions.

6. Community and Ecosystem: Memcached has a large and active community of users and developers. It is widely used and supported by many programming languages and frameworks. Integration with applications is straightforward, and there is ample documentation available. Varnish also has a thriving community but is more commonly used in specific use cases, such as content-heavy websites or as a cache in front of web servers. It offers a range of extensions and modules, but its ecosystem is not as extensive as that of Memcached.

In summary, Memcached and Varnish differ in their scalability approaches, caching mechanisms, cache invalidation capabilities, CDN support, request processing abilities, and community ecosystems. Understanding these differences is crucial in selecting the appropriate caching system for specific use cases.