Editing Web server (section)

==== Dynamic cache ====
Dynamic content, output by an internal module or an external program, may not always change very frequently (given a unique URL with keys / parameters) and so, maybe for a while (e.g. from 1 second to several hours or more), the resulting output can be cached in RAM or even on a fast [[Disk storage|disk]].<ref name="ws-disk-cache-apache">{{Cite web|url=https://httpd.apache.org/docs/2.4/mod/mod_cache_disk.html|title=Apache Module mod_cache_disk|publisher=Apache: HTTPd server project|year=2021|access-date=2021-12-09|language=en|archive-date=9 December 2021|archive-url=https://web.archive.org/web/20211209211241/https://httpd.apache.org/docs/2.4/mod/mod_cache_disk.html|url-status=live}}</ref>

The typical usage of a dynamic cache is when a website has [[dynamic web page]]s about news, weather, images, maps, etc. that do not change frequently (e.g. every ''n'' minutes) and that are accessed by a huge number of clients per minute / hour;  in those cases it is useful to return cached content too (without calling the internal module or the external program) because clients often do not have an updated copy of the requested content in their browser caches.<ref name="ws-dynamic-cache-edu">{{Cite web|url=https://www.educative.io/edpresso/what-is-dynamic-cache|title=What is dynamic cache?|publisher=Educative|author=|year=2021|access-date=2021-12-09|language=en|archive-date=9 December 2021|archive-url=https://web.archive.org/web/20211209234355/https://www.educative.io/edpresso/what-is-dynamic-cache|url-status=live}}</ref>

Anyway, in most cases those kind of caches are implemented by external servers (e.g. [[reverse proxy]]) or by storing dynamic data output in separate computers, managed by specific applications (e.g. [[memcached]]), in order to not compete for hardware resources (CPU, RAM, disks) with web server(s).<ref name="ws-dynamic-cache-tut">{{Cite web|url=https://www.siteground.com/tutorials/supercacher/dynamic-cache/|title=Dynamic Cache Option Tutorial|publisher=Siteground|author=|year=2021|access-date=2021-12-09|language=en|archive-date=20 January 2023|archive-url=https://web.archive.org/web/20230120185251/https://www.siteground.com/tutorials/supercacher/dynamic-cache/|url-status=live}}</ref>
<ref name="ws-dynamic-cache-std">{{Cite web|url=https://www.researchgate.net/publication/2585583|title=Improving Web Server Performance by Caching Dynamic Data|publisher=Usenix|author1=Arun Iyengar|author2=Jim Challenger|year=2000|access-date=2021-12-09|language=en}}</ref>