nosql
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The Apache Cassandra database is the right choice when you need scalability and high availability without compromising performance. Linear scalability and proven fault-tolerance on commodity hardware or cloud infrastructure make it the perfect platform for mission-critical data. Cassandra's support for replicating across multiple datacenters is best-in-class, providing lower latency for your users and the peace of mind of knowing that you can survive regional outages. Cassandra's ColumnFamily data model offers the convenience of column indexes with the performance of log-structured updates, strong support for materialized views , and powerful built-in caching. Cassandra is in use at Netflix , Twitter , Urban Airship , Constant Contact , Reddit , Cisco, OpenX, Digg, CloudKick, Ooyala, and more companies that have large, active data sets. The largest known Cassandra cluster has over 300 TB of data in over 400 machines.
The Apache Cassandra Project
orient - Project Hosting on Google Code
What is Orient? OrientDB is an Open Source NoSQL DBMS with both the features of Document and Graph DBMSs. It's written in Java and it's amazing fast: can store up to 150,000 records per second on common hardware.