Stale-while-revalidate Cache Invalidation

Why Cache Invalidation is Important?

By keeping a copy of frequently accessed material in memory or on a disc, the concept of caching allows users to retrieve that data more quickly. However, the cached copy could grow outdated or erroneous if the original data changes. Incorrect results or performance issues may ensue if the application keeps using the cached data. When the original data changes, the process of invalidating a cache involves deleting or updating cached data....

Cache Invalidation Methods

Cache invalidation is an important process for maintaining accurate and up-to-date data in a cache. There are several methods of cache invalidation, each with its own advantages and disadvantages. Here are a few of the most popular techniques:...

1. Time-based Cache Invalidation

Time-based invalidation involves setting an expiration time for cached data.  The cached data must be refreshed from the source once the expiration time has passed because it is then deemed invalid. This approach is straightforward to use and useful for data that doesn’t change frequently. However, if the expiration time is set too long or too short, it might result in the use of stale data or unneeded refreshes....

2. Key-based Cache Invalidation

Key-based invalidation involves associating a unique key with each piece of cached data. The associated key is invalidated when the original data is altered, and the cached data is either deleted or updated. This approach can guarantee that the most recent data is always used and is effective for data that changes frequently. It might be trickier to put into practice than time-based invalidation, though, and more key storage space might be needed....

3. Write-through Cache Invalidation

Write-through invalidation involves updating the original data source first and then updating or removing the cached data. By using this technique, the risk of stale data is decreased and the cached data is always current. The application must wait for the primary data source to be updated before updating the cache, so it can be slower than other approaches....

4. Write-behind Cache Invalidation

Write-behind invalidation involves updating the cached data first and then updating the original data source. Due to the lack of a wait time for the application, while the original data source is updated, this approach may be quicker than write-through invalidation. Because the cached data might not always be in sync with the original data source, it can, however, increase the risk of stale data....

5. Purge Cache Invalidation

By using the purge method, cached content for a particular object, URL, or collection of URLs is deleted. When the content has been updated or changed and the cached version is no longer accurate, it is typically used. The cached content is immediately deleted in response to a purge request, and the following request for the content will be fulfilled by the origin server directly....

6. Refresh Cache Invalidation

Even if there is cached content available, fetches the requested content from the origin server. The cached content is updated with the most recent version from the origin server in response to a refresh request, making sure the content is current. A refresh request, in contrast to a purge, updates the existing cached content with the most recent version rather than erasing it....

7. Ban Cache Invalidation

A URL pattern or header is an example of specific criteria that the ban method uses to invalidate cached content. Any cached content that meets the requirements of a ban request is immediately removed, and any ensuing requests for the content will be fulfilled directly by the origin server....

8. Time-To-Live(TTL) expiration Cache Invalidation

With this technique, cached content is given a time limit after which it becomes stale and needs to be refreshed. The cache checks the time-to-live value when a request for the content is made and only serves the cached content if the value is still valid. The cache gets the most recent copy of the content from the origin server and caches it if the value has expired....

9. Stale-while-revalidate Cache Invalidation

Web browsers and CDNs employ this technique to serve out-of-date content while it is being updated in the background. When someone requests a piece of content, the cached copy is delivered right away, and an asynchronous request is sent to the origin server to get the most recent copy. The cached version is updated when the most recent version becomes available. The user is always quickly served content thanks to this technique, even if the cached version is slightly out of date....