I’m sure everyone has visited Craigslist at least once since its launch in 1995. Although at that early stage it was just an email distribution list among a small group of people about different local events and activities. However since then it has grown into one of the most visited English websites, with local classified in over 450 cities world wide. You can look for classifieds in virtually any category imaginable and it also has discussion boards for different relevant topics. Just today I visited Craigslist in search of a hairdresser, and found one at a relatively good price.
Craigslist uses a few different engines for their database needs, including MySQL, Redis, MongoDB, and Sphinx. Craigslist stores such a vast amount of data that the combination of these many databases helps keep up with all of it, without slowing everything down. Redis allows the metadata search engines for the site and is multi-core allowing for more instances to be ran at a time. Sphinx offers full text indexing and searches of all postings, live and archived, as well as current forums. MySQL allows clusters, so they are able to store posting, finances, users, stats, etc. in one database. So as you can see this rather small company uses all the resources available to them to keep a simple and seamless website.