[sumtechguy]

There is a perf hit. You can not help it when you are slugging that many bytes around. An int/int64 fits into a register easy and the instruction for comparison is cheap. However, when you add in replication and other items UUID becomes more desirable due to the property having extra information embedded into it to make them unique. You can get some of the same benefits with more complexity if you are using auto increment. Such as using a stride that is similar to the number of machines you have in the cluster. But even that can get weird, and depending on your db can be a pain to setup. Using them as a cluster index and you probably will most certainly create a hotspot index and poor lookup performance, but decent write. Just due to the fact that items probably are not grouped the same as your where clause. SSD's have hidden most of this for most databases. But the issues are the same.