mainly marketing articlle by cofiiunder What if you didn't have to do any of this funny business to get scalability and reliability? What if the JVM had access to a service that you could plug into to make its heap durable, arbitrarily large, and shared with every other JVM in your application tier? Enter Terracotta, network-attached, durable virtual heap for the JVM. In the spirit of full-disclosure, I'm a co-founder of Terracotta and work there as a software developer. Terracotta is an infrastructure service that is deployed as a stand-alone server plus a library that plugs into your existing JVMs and transparently clusters your JVM's heap. Terracotta makes some of your JVM heap shared via a network connection to the Terracotta server so that a bunch of JVMs can all access the shared heap as if it were local heap. You can think of it like a network-attached filesystem, but for your object data; see Figure 1.
Redis is a key-value database. It is similar to memcached but the dataset is not volatile, and keys can be strings, exactly like in memcached, but also lists and sets with atomic operations to push/pop elements. In order to be very fast but at the same time persistent the whole dataset is taken in memory and from time to time and/or when a number of changes to the dataset are performed it is written asynchronously on disk. You may lost the last few queries that is acceptable in many applications but it is as fast as an in memory DB (btw the SVN version of Redis includes support for replication in order to solve this problem by redundancy). Replication and other interesting features are a work in progress (Basic master <-> slave replication implemented in Redis SVN). Redis is written in ANSI C Redis is pretty fast!, 110000 SETs/second, 81000 GETs/second in an entry level Linux box.
James Hamilton has published a thorough summary of Facebook's Cassandra, another scalable key-value store for your perusal. It's open source and is described as a "BigTable data model running on a Dynamo-like infrastructure." Cassandra is used in Facebook as an email search system containing 25TB and over 100m mailboxes. # Google Code for Cassandra - A Structured Storage System on a P2P Network # SIGMOD 2008 Presentation. # Video Presentation at Facebook # Facebook Engineering Blog for Cassandra # Anti-RDBMS: A list of distributed key-value stores # Facebook Cassandra Architecture and Design by James Hamilton