/directory1/directory2 To: /directory1/directory2/ Example 2: a whole set of documents has been moved inside website in order to reorganize their file system paths. From: /directory1/directory2/2021-10-08/ To: /directory1/directory2/2021/10/08/ Example 3: a whole set of documents has been moved to a new website and now it is mandatory to use secure HTTPS connections to access them. From: http://www.example.com/directory1/directory2/2021-10-08/ To: https://docs.example.com/directory1/2021-10-08/ Above examples are only a few of the possible kind of redirections. Successful message A web server program is able to reply to a valid client request message with a successful message, optionally containing requested web resource data. If web resource data is sent back to client, then it can be static content or dynamic content depending on how it has been retrieved (from a file or from the output of some program / module). Content cache In order to speed up web server responses by lowering average HTTP response times and hardware resources used, many popular web servers implement one or more content caches, each one specialized in a content category. Content is usually cached by its origin, e.g.: static content: file cache; dynamic content: dynamic cache (module / program output). File cache Historically, static contents found in files which had to be accessed frequently, randomly and quickly, have been stored mostly on electro-mechanical disks since mid-late 1960s / 1970s; regrettably reads from and writes to those kind of devices have always been considered very slow operations when compared to RAM speed and so, since early OSs, first disk caches and then also OS file cache sub-systems were developed to speed up I/O operations of frequently accessed data / files. Even with the aid of an OS file cache, the relative / occasional slowness of I/O operations involving directories and files stored on disks became soon a bottleneck in the increase of performances expected from top level web servers, specially since mid-late 1990s, when web Internet traffic started to grow exponentially along with the constant increase of speed of Internet / network lines. The problem about how to further efficiently speed-up the serving of static files, thus increasing the maximum number of requests/responses per second (RPS), started to be studied / researched since mid 1990s, with the aim to propose useful cache models that could be implemented in web server programs. In practice, nowadays, many popular / high performance web server programs include their own userland file cache, tailored for a