I think it also depends on how you structure your database and how you use it. For some things a NOSQL design is great and most of them don't have to lock over

I think it also depends on how you structure your database and how you use it. For some things a NOSQL design is great and most of them don't have to lock over multiple tables they might be very fast at getting structured records. They might be terrible if you try to join different records (especially if they are located on different shards) and some don't have ACID if that is a requirement. Some databases like Datomic stores information in a completely different way that may be very fast for some use cases. If you have an application or a specific use case you can try a few different databases and measure how they work. I tried a small memory database and got much better performance than SQL Server gave me while the queries were easier to write, for other things this database would not have worked at all or it might have been about as fast as a relational db. As a general rule the memory db providers seems to make the case that they are faster than normal relational databases. Take a look at VoltDb or StarCounter for example.