> Cassandra and MongoDB are completely fine as general purpose databases.
Whenever I hear this, I feel that the person saying it either doesn't have enough experience or that every problem to them looks like a nail for their particular flavor of NoSQL. That's like saying a street bike is a general purpose bicycle. I'm sure someone out there can make it work on an outdoor offroad trail, but is it ideal?
Cassandra is really awesome at writes but reads are really expensive. Atomicity at the row level only (unless you want that 30% performance hit) and eventually consistency make this not great at real time. CQL3 is an improvement but it's still not as good as ANSI SQL. I still have to do a lot of extra work.
With Mongodb it does really well with tree based data. The second you try to do join queries outside of that doc tree... major performance hit. (Maybe this has changed knowing the speed mongo evolves.) When data is larger than RAM... major performance hit... not so great for something like logging.
Using an RDBMS for everything isn't great, but the pain you suffer is a lot less especially since these days more and more them have some sort of federation or cluster solution. That said, some NoSQL datastores are better for certain applications than an RDBMS, just not for all of them.
Whenever I hear this, I feel that the person saying it either doesn't have enough experience or that every problem to them looks like a nail for their particular flavor of NoSQL. That's like saying a street bike is a general purpose bicycle. I'm sure someone out there can make it work on an outdoor offroad trail, but is it ideal?
Cassandra is really awesome at writes but reads are really expensive. Atomicity at the row level only (unless you want that 30% performance hit) and eventually consistency make this not great at real time. CQL3 is an improvement but it's still not as good as ANSI SQL. I still have to do a lot of extra work.
With Mongodb it does really well with tree based data. The second you try to do join queries outside of that doc tree... major performance hit. (Maybe this has changed knowing the speed mongo evolves.) When data is larger than RAM... major performance hit... not so great for something like logging.
Using an RDBMS for everything isn't great, but the pain you suffer is a lot less especially since these days more and more them have some sort of federation or cluster solution. That said, some NoSQL datastores are better for certain applications than an RDBMS, just not for all of them.