​Akamai​ 's Fast Purge supports two different methods. When you purge your cached content by URL, ARL, CP code or cache tag, you select either Invalidate or Delete. Enhanced purge (ECCU) only invalidates content. It doesn't remove it from cache.

Invalidate

This purge method marks the cached content as invalid. The next time the ​Akamai​ edge server receives a request for the content, it sends an HTTP conditional GET request with the If-Modified-Since header to the origin. If the content has changed or the origin doesn't support Last-Modified headers, the origin server returns a full fresh copy. Otherwise, the origin normally verifies that the content hasn't changed, and ​Akamai​ can serve the already-cached content.

Delete

This purge method removes the content from the ​Akamai​ edge server cache. The next time the edge server receives a request for the content, it retrieves the current version from the origin server. If it can't retrieve a current version, it follows the instructions you specified in the configuration. Use delete for compliance or copyright-related purge requests, as it completely removes all content from the servers.

What's the difference?

Invalidate is the default and most popular behavior. It removes objects from cache and retrieves full objects from your origin only if they are newer than the cached versions. The delete method can increase the load and bandwidth on your origin more than invalidate because delete retrieves the full object from the origin every time. When configured to do so, invalidate also allows the ​Akamai​ edge server to continue to serve stale content to your end users if the origin is unreachable.

Either of the purge request methods don't persist. The edge server executes a request and then "forgets it."