1. Shujaat Hussain

9. A single column

10. A single row

17.  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)

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

19.  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’ ”

20.  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.

21.  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

22.  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

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

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

25.  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