That's what we hear from our customers as well. They complain about excessive CPU and memory usage.
The two phases we've seen are:
1/It's flexible and it works! Problem solved!
2/21st century called, they want their performance back.
The problem with phase 2 is that you may not be able to solve it by throwing more computing power at it.
Unfortunately if you really need map-reduce, at the moment I don't know what to recommend. Riak isn't better performance-wise and our product doesn't support map-reduce (yet).
However if you don't need map-reduce I definitively recommend not using Cassandra. There's a lot of non-relational databases out there that are an order of magnitude faster.
The two phases we've seen are:
1/It's flexible and it works! Problem solved! 2/21st century called, they want their performance back.
The problem with phase 2 is that you may not be able to solve it by throwing more computing power at it.
Unfortunately if you really need map-reduce, at the moment I don't know what to recommend. Riak isn't better performance-wise and our product doesn't support map-reduce (yet).
However if you don't need map-reduce I definitively recommend not using Cassandra. There's a lot of non-relational databases out there that are an order of magnitude faster.