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    <p>Facebook didn't <em>move</em> to Cassandra, they created it. :) To my knowledge, noSQL DBMSes don't require <strike>or even mention</strike> (thanks to mnemosyn for the correction, Facebook uses Oracle and Cassandra) running side by side with a relational database. <a href="http://degizmo.com/2010/03/24/redis-relations-in-a-nosql-world-using-hashes/" rel="nofollow noreferrer">This</a> is one opposite example (storing user information in a noSQL DB).</p> <p>I would say that if Cassandra is good enough for Facebook, it's likely to be good enough for your project. It might not hurt to try to abstract the persistence logic so that you have the possibility to switch to something else, if it absolutely comes to that.</p> <p>Disclaimer: I have not (yet?) had any hands on experience with noSQL databases: what I know comes from reading about it.</p>
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    1. POCassandra instead of MySQL for social networking app
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    1. USTomislav Nakic-Alfirevic
    1. USTomislav Nakic-Alfirevic
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    1. COIt seems you're mixing up concepts here: NoSQL is a very abstract term and contains both ACID databases which have basically the same guarantees as typical RDBMS have (e.g. db4o) as well as databases that scale, but don't offer the same set of guarantees (e.g. cassandra) when it comes to data consistency. These properties should be the guide for decisions. Abstracting this kind of logic is impossible, I believe: There's a significant difference in data you can trust, and data you can't trust. Transactions might not make sense, etc.
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      1. USmnemosyn
    2. COAbstracting what kind of logic? ACID transactions? The DB either supports or does not support them: what I was talking about is basically providing e.g. a thin DAO layer above the database so that the part of the application above the DAO layer can remain more or less intact if the DAO implementation changes (due to a move to a different DB). As for choosing which database, Christopher described the project as having "very similar features to Facebook" so it would be quite peculiar if it turned out that it would be better for Christopher to use a database different than the one Facebook uses.
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      1. USTomislav Nakic-Alfirevic
    3. COFacebook doesn't use one database. They use (at least) Oracle, Cassandra and Hadoop in parallel. Cassandra was developed for searching your inbox on facebook, not for storing payment details. You cannot put the same abstraction on different things, i.e. use one DAO for data store that is consistent and one that is only eventually consistent.
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