Shujaat Hussain

A single column

A single row

 Consistency –the system is in a consistent state after an operation  Availability –the system is “always on”, no downtime  Partition tolerance–the system continues to function even when split into disconnected subsets (by a network disruption)

 MySQL  300ms write  350ms read  Cassandra  0.12ms write  15ms read

 You need a key or keys:  Single: key=‘a’  Range: key=‘a’ through ’f’  And columns to retrieve:  Slice: cols={bar through kite}  By name: key=‘b’ cols={bar, cat, llama}  Nothing like SQL “ WHERE col=‘faz’ ”

 Digg is a social news site that allows people to discover and share content from anywhere on the Internet by submitting stories and links, and voting and commenting on submitted stories and links.

 Problems  Terabytes of data; high transaction rate (reads dominated)  Multiple clusters  Management nightmare (high effort, error prone)  Unsatisfied availability requirements (geographic isolation)  Solution  Cassandra as primary data store  Datacenter and rack-aware replication

 Twitter is a social networking and microblogging service that enables its users to send and read tweets, text-based posts of up to 140 characters.  Terabytes of data, ~1,000,000 ops/s

 Inbox Search  100 TB  160 nodes  1/2 billion writes per day (2yr old number?)

 Advantages  Massive scalability  High availability  Lower cost (than competitive solutions at that scale)  (usually) predictable elasticity  Schema flexibility, sparse & semi-structured data

 Disadvantages  Limited query capabilities (so far)  Eventual consistency is not intuitive to program for  Makes client applications more complicated  No standardizatrion  Portability might be an issue  Insufficient access control