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NOSQL & DISTRIBUTED DATA

NoSQL & Distributed Data: Scaling Beyond Single Nodes

DOWNLOADING CONCEPT: 1. THE CAP THEOREM...
  • ↳The absolute foundation of distributed databases.
  • ↳In any distributed data store, you can only pick TWO of the following three guarantees:
  • ■Consistency (C): Every read receives the most recent write (or an error). All clients see the same data at the same time.
  • ■Availability (A): Every request receives a non-error response (but without the guarantee that it contains the most recent write).
  • ■Partition Tolerance (P): The system continues to operate despite network failures (partitions) between nodes.

↳Because network failures (P) are unavoidable in the real world, you are effectively forced to choose between CP (Consistency + Partition Tolerance) or AP (Availability + Partition Tolerance).

▲ LIVE INCIDENTA distributed e-commerce cart system backed by Cassandra is experiencing 'zombie items'. Users delete an item from their cart, but it reappears an hour later!
sre@arena:~/nosql-distributed
sre@arena:~$ nodetool tpstats | grep -i dropped