HBase at Facebook and Why Not MySQL or Cassandra
Jeremiah Peschka on:
What makes this decision interesting is not just the reasons that Apache HBase was chosen, but also the reasons that MySQL and Cassandra were not chosen.
Briefly:
- not MySQL: because sharding can be very difficult at the scale of Facebook messages system
- not Cassandra: because of replication behavior

Update: There were a few pointing out that the original article is inaccurate. Todd Lipcon’s comment is providing some corrections pretty much demoting all technical arguments in the post. Todd concludes:
That said, the point about existing operational experience with Hadoop and HDFS is absolutely correct. There is a large Hadoop team at Facebook and they are truly experts in the technology. The HBase team there is also growing quickly and have been great contributors in the last several months.
Original title and link: HBase at Facebook and Why Not MySQL or Cassandra (NoSQL databases © myNoSQL)
via: http://facility9.com/2010/11/18/facebook-messaging-hbase-comes-of-age