The article basically comes right out and says it. You just need to read between the lines a little bit.
From the article:
Quinn was the main champion of moving over to Cassandra, say our sources. Now the site is taking a huge hit, at least in the short term, because of that decision and/or how it was implemented, and Quinn is paying for it with his job.
It's always a toss up between whether it was implemented correctly or not. The correct course of action of course would have been to slowly move the site over to the new technology piece by piece rather than a wholesale switchover. The risk is in the migration strategy not the technology picked. They could have been equally stupid switching over to a new architecture with mysql.
From the article: Quinn was the main champion of moving over to Cassandra, say our sources. Now the site is taking a huge hit, at least in the short term, because of that decision and/or how it was implemented, and Quinn is paying for it with his job.
It's always a toss up between whether it was implemented correctly or not. The correct course of action of course would have been to slowly move the site over to the new technology piece by piece rather than a wholesale switchover. The risk is in the migration strategy not the technology picked. They could have been equally stupid switching over to a new architecture with mysql.