Linux Database Server CPU Comparison

Analyses and Conclusion

First of all, we would like to emphasize that we are well aware of our findings - they are only applicable to your database applications if you run a "read heavy, few writes" database server and the database is not too large, so the most used parts can run mainly from the RAM. As 1 GB DIMMs are very cheap now and with the introduction of 64 bit CPUs and 64 bit Linux 2 years ago, it is clear that making sure that your database has enough memory for its disposal should become a lot easier for many database administrators.

There are a few interesting conclusions that we can make about the software side of things. First of all, DB2 8.2 scales fantastic when you add more CPUs. This makes the dual core Opterons very attractive: an Opteron 265 costs as much as an Opteron 252 or Xeon Irwindale 3.6 GHz, but it is clear that it will perform a lot better. It also offers a better upgrade path, since you can use up to four cores on relatively cheap motherboards - compared to the average price of a quad CPU motherboard - with two sockets.

The MySQL MyISAM benches make it clear that pure speed isn't everything. MySQL MyISAM allows you to get away with a single CPU system as it delivered up 300 queries per second, while DB2 was only capable of delivering a bit more than one third of that performance. The picture quickly changes when we need safe transactions too (even with few writes, this might be critical): the InnoDB engine is about 40% slower in our environment. MySQL remains very fast, but as we add more CPUs, the difference gets very small with DB2. While this article has no ambition to be a guide to the software part of database servers, it is clear that you should choose your hardware in function of the database server software that you select. With DB2, you get enterprise class database serving, and dual core CPUs are a very good solution for it. MySQL is excellent to save on your hardware costs, but if you expect the number of transactions/data mining queries to rise quickly, adding more than two CPUs will buy you little performance (10 to 20% boost).

The most surprising thing that we noticed while comparing our new findings on the 2.6 kernel with those of our previous report (32 bit, 2.4 kernel) is that the Xeon benefits a lot less from 64 bit and the new 2.6 kernel than the Opteron. While the 64 bit binaries run consistently (much) faster on the Opteron, the Xeon isn't too happy with them and runs them 4 to 10% slower. Hyperthreading isn't - in our case - helping either, with 1 to 10% lower performance.

Branch prediction penalties, due to the longer pipeline of Nocona/Irwindale, are not the problem. We noticed with Vtune and Code Analyst that the Branch Prediction Unit of the Xeon Nocona and Irwindale does a marvellous job and predicts between 96% (MySQL) and 97% (DB2) of the branches correctly, while the Opteron's BPU is about 93% and 94% correct of the time. MySQL consists of 20% branches, and DB2 has only 16% branches. The L2-caches also do a good job with only 2% of data demands being covered by the RAM, and a 98% hitrate on the L1 and L2-caches.

According to our research, we can assume that the 64 bit implementation of the new Xeon is simply not as powerful as the Opteron's. Intel has some catching up to do, especially when you look at the dual core Opterons. We already discussed AMD's elegant dual core architecture in detail, but in this review, we have seen very good indications that the design with the two cores connected by the SRQ does improve performance in real world applications and not only in our cache-to-cache tests.

This architecture together with AMD being six months ahead with their dual core server product gives AMD significant advantages in the server market today. The lack of mature server versions of Windows (2003) and the fact that only the latest kernels of Linux support the dual core Opteron might slow AMD a bit down, but not for long.