RESTBase/Table storage backend options

This page was created in November 2014 to collect details on possible backends for the RESTBase table storage layer. As a result of the evaluation, Cassandra was deployed to the Wikimedia infrastructure. See Cassandra for more information about Wikimedia's current deployment, and see T76157 for discussion about the evaluation.

Exclusion criteria
These criteria need to be satisfied by candidates:
 * No single point of failure
 * horizontal read scaling: can add nodes at any time; can increase replication factor
 * horizontal write scaling: can add nodes at any time
 * Has been hardened by production use at scale