can more CPU introduce performance issues?

I was talking to my managers about the new hardware configurations and I mentioned that for test like readprobe, more CPU can introduce issues,and I think everyone of them was holding their breath and thinking "what is this guy talking about?". but the fact is that more CPU don't always means better performance.

I am going to type out my thoughts and try to clear this out just for myself. As we know after 10.2B06, the LRU latch can almost be "eliminated" from your list of concerns. As long as the response time and the buffer hit ratio are acceptable for your users and your DBA, you are in good shape in that front. However, that doesn't mean we are all done with database tuning, that just means that we are transferring the bottleneck to somewhere else, and in this case, the BHT. The buffer hash table, Progress does not recommend you to tune the -hash value, it uses 25% of the -B as a good measure and it works out well for most of the applications. BHT, is the lookup table to quickly lookup values within the buffer and the number of entries in that table is relative small, especially when we are talking about the sports database. The modern CPU is fast, 3.0G is a not exceptions, but that is a very fast processor. Also the modern CPUs are mostly in SMT or CMT model for multi-threading, a 32 core machine is not uncommon. When all the CPUs are lining up to lookup the tables, and only one lucky process can access this resource at any given time, that can lead to congestion, if they are all interested in somewhat similar or same data, they traffic jam is not hard to imagine. So the CPUs take a nap after they finish spinning, and wake up, keep spinning. At the same time, they are taking up the CPU resources and get nothing done, we have a BHT contention. Not mentioning the number of context switches this can introduce which add another layer of system usage instead of user usage.

So there is a balance of the how fast the lookup can be done and how many CPU are lining up for this resource.