Lemmy is incredibly unique in it's stance of not using Redis, Memcached, dragonfly... something. And all the CPU cores and RAM for what this week is reported as 57K active users across over 1200 Instance servers.
Why no Redis, Memcached, dragonfly? These are staples of API for scaling.
Anyway, Reddit too started with PostgreSQL and was open source.
MONDAY, MAY 17, 2010
http://highscalability.com/blog/2010/5/17/7-lessons-learned-while-building-reddit-to-270-million-page.html
"and growing Reddit to 7.5 million users per month"
Lesson 5: Memcache
The essence of this lesson is: memcache everything.
They store everything in memcache: 1. Database data 2. Session data 3. Rendered pages 4. Memoizing (remember previously calculated results) internal functions 5. Rate-limiting user actions, crawlers 6. Storing pre-computing listings/pages 7. Global locking.
They store more data now in Memcachedb than Postgres. It’s like memcache but stores to disk. Very fast. All queries are generated by same piece of control and is cached in memcached. Change password Links and associated state are cached for 20 minutes or so. Same for Captchas. Used for links they don’t want to store forever.
They built memoization into their framework. Results that are calculated are also cached: normalized pages, listings, everything.