Application Caching #

Application caching improves the responsiveness of a request by storing commonly used results from queries into fast in-memory systems.

This relieves the database from heavy read traffic.

Application-level caching is also known as the cache-aside pattern. Meaning the application effectively bypasses persistent storage and goes directly to the cache.

Other caching patterns include:

• Read-through - All read requests are accessed through the cache. If a cache-miss occurs, the caching system invokes a loader function to fetch and load the data from the persistent storage to the cache.
• Write-through - Writes and updates happen to both the cache and the persistent storage. Whenever an update occurs to the cache, the caching system invokes a writer to update the database as well. The request only completes when both the cache and the persistent storage are updated.
• Write-behind - Like write-through but the application does not wait for the database to be updated when the cache updates.

Web Caching #

Web caches store a copy of a given resource for a defined time period in places such as the browser (private cache) or by the Organization and ISP (shared caches).

Caches typically store the results of GET requests only where the cache key is the URI associated with the request.

Content Delivery Networks (CDNs) #

Edge caches (aka CDNs) are strategic content delivery sites that live in various geographical areas.

HTTP Caching Directives #

Services can control what results are cached and for how long they are stored using HTTP caching directives.

Some of these directives are the following:

Cache-Control #

The Cache-Control HTTP header can be used by client requests and service responses to specify how the caching should be utilized for the resources.

Expires and Last-Modified #

The Expires and Last-Modified HTTP headers interact with the max-age directive to control how long cached data is retained.

This is used for cache invalidations.

Etag #

An Etag is an opaque value that can be used by a web cache to check if a cached resource is still valid.