Exactly- using Twitter's problems on Rails as evidence it doesn't scale is only slightly more wrong than blaming on them on MySQL. Twitter started moving to Cassandra in 2010 to deal with scaling issues they were having with MySQL sharding (gizzard), but continued to release patches to MySQL to address their needs, then eventually created their own data store, Manhattan, optimized for their particular usage patterns. None of this means MySQL (or Rails) can't scale.

> The biggest problem Twitter had was using MySQL for data storage.

Sorry but I find this part contradictory.

And the argument that follows sounds like backpedaling.

Twitter ended up ditching Rails anyways despite "fixing" their data storage. So to me their problem was indeed Rails.

MySQL was the biggest problem they had though! They brought in Lucene (Earlybird) that massively improved performance- which makes a lot of sense.(in addition to adding Cassandra and eventually manhattan).

Then they started building a lot of things that weren't web applications, like RPC servers (where they created the finagle library) they ended up with a team where Scala and the JVM was more their area of expertise and interest and solution to every issue.

No one thinks you use MySQL to build every kind of data application, no one thinks you use Rails to build every kind of server.