I've been studying cassandra recently and would like to share my findings.
What is cassandra?
Apache Cassandra is an open source, distributed, decentralized, elastically scalable, highly available, fault-tolerant, tuneably consistent, column-oriented database.
Cassandra is an open source distributed database management system. It is designed to handle very large amounts of data spread out across many commodity servers while providing a highly available service with no single point of failure.
Cassandra provides a structured key-value store with eventual consistency. Keys map to multiple values, which are grouped into column families. The column families are fixed when a Cassandra database is created, but columns can be added to a family at any time. Furthermore, columns are added only to specified keys, so different keys can have different numbers of columns in any given family. The values from a column family for each key are stored together, making Cassandra a hybrid between a column-oriented DBMS and a row-oriented store.
where is cassandra use?
well, you can store whatever you want, for example, we used cassandra to store the call detail record.
where do i get started to learn cassandra?
i suggest you start with a cassandra book for beginner or person coming from RDBMS. Because there are new terminology with is introduced in cassandra. When you get a hold on cassandra, you should really get the source from apache cassandra website and they have a great information in their wiki page.
where do i get help if i have question?
they have mailing list where you can find if your question is asked before or you can contact me. :-)