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MongoDB vs. Cassandra

I have been reading articles about Cassandra vs MongoDB lately but could not decide which one to choose; the articles were more than a year old or they didn't answer my questions.

I will be designing an online game with really large data sets (maybe live feed) so I need scalability and speed.

Which one you would choose? Or, what are the strengths and weaknesses?

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Ataman
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  • Jumping to NoSql is the cool thing to do but are you sure MySql (or another RDMS) cant handle the queries? And another question is how reliable do you need data to be, because remember Cassandra is [eventually consistent](http://stackoverflow.com/questions/4584353/meaning-of-eventual-consistency-in-cassandra). – Lyuben Todorov Nov 05 '12 at 15:11
  • @LyubenTodorov Yes I considered mysql but it will have very high number of transactions because of the high number of users and data. Also system should be reliable because of being a game.. Thanks for the comment. – Ataman Nov 05 '12 at 15:25
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    thats correct but in two years a lot may have changed. Thats why i wanted to see an updated answer. And i believe nosql has grown crazy in the last two years. @Pangea – Ataman Nov 05 '12 at 15:34
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    @user446141 If you need the system to be perfectly reliable than Cassandra might have short falls depending on what replication factor you choose, and even with a factor of 1, data is still not 100% consistent (users could get out-of-date data), however if you have a single node cluster (pointless as it removes the scalability factor) data would always be consistant. – Lyuben Todorov Nov 05 '12 at 15:35
  • Thanks @LyubenTodorov that was very helpful. Any comment on consistency in MongoDB? – Ataman Nov 05 '12 at 15:38
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    @user446141 I lack experience when it comes to MongoDB's consistency, I know there are some edge cases where data is out-of-date but they are rare compared to Cassandra. Mongo wont be as goot at it as RDMS' (they were built for data consistency) however im not completely sure but there is a [visual representation](http://maxivak.com/wp-content/uploads/2011/07/media_httpfarm5static_mevIk.png) that is more to the point. – Lyuben Todorov Nov 05 '12 at 15:44
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    @Lyuben Todorov the consistency level in Cassandra is tunable on a per-request basis. You can have completely consistent reads and writes *when you need them* and accept eventual consistency (for performance) for other operations. – DNA Nov 06 '12 at 20:57

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