Why aren't NoSQL Databases ACID compliant? [duplicate]

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Possible Duplicate:
Is there any NoSQL that is ACID compliant?

So, I heard NoSQL Databases are not ACID compliant, why is this?

Answer 1

This isn't necessarily true - it depends on which particular database you're referring to. Some of them (for example Neo4j) are fully ACID compliant. Check out this link for a comparison of some NoSQL databases: http://kkovacs.eu/cassandra-vs-mongodb-vs-couchdb-vs-redis

Answer 2

Generally speaking, ACID compliance imposes performance overhead. NoSql performance is enhanced by this lack of performance overhead.