This document summarizes Cassandra adoption and use cases at Expedia over time. In 2011, Expedia implemented Cassandra for pricing indexes, session state caching, and transaction logging. In 2012, they upgraded to DataStax and expanded Cassandra's use to additional pricing indexes, search via SOLR, and high-speed transaction logging. For pricing indexes, Expedia moved from a 9-node Cassandra cluster to a 27-node cluster with DataStax to support more markets and elements. For logging, they moved from SQL servers to a 72-node DataStax cluster with Hadoop for reporting, reducing costs by $1.5M. By the end of 2012, Expedia planned to have 240 DataSt