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Selecting a Processor for SQL Server 2014 – Part 2

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Paul White is an independent SQL Server consultant specializing in performance tuning, execution plans, and the query optimizer.

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Back in January, I wrote Selecting a Processor for SQL Server 2014 – Part 1. Now, with the recent announcement of a General Availability (GA) date of April 1, 2014 for SQL Server 2014, it is time to cover part two of this series.

Four-Socket Servers

The big news since January is the release of the new 22nm Intel Xeon E7-4800 v2 Product Family (Ivy Bridge-EX) processors on February 16, 2014. Currently, there are eight different processors in this product family. If you think about how SQL Server 2014 core-based licensing works, and you want the best performance possible for the lowest license cost, you can pretty quickly narrow down that list to just three interesting processors for SQL Server. These are the fifteen-core Xeon E7-4890 v2, the twelve-core Xeon E7-4860 v2, and the ten-core Xeon E7-4830 v2. Table 1 shows some of the relevant specifications for these three processors.

Model Cores Base Speed Turbo Speed L3 Cache Size Cost
E7-4890 v2 15 2.8GHz 3.4GHz 37.5MB $6,619.00
E7-4860 v2 12 2.6GHz 3.2GHz 30MB $3,838.00
E7-4830 v2 10 2.2GHz 2.7GHz 20MB $2,059.00

Table 1: Recommended Xeon E7-4800 v2 Processor Models for SQL Server 2012/2014

Intel has two lower-cost, fifteen-core models in the family (the Xeon E7-4880 v2 and the Xeon E7-4870 v2), but both of these have pretty significant reductions in clock speed and/or L3 cache size. They also have a lower-cost twelve-core model (the Xeon E7-4850 v2) that has a significant reduction in clock speed and L3 cache size. Finally, there is a low-cost eight-core Xeon E7-4820 v2 and a low-cost six-core Xeon E7-4809 v2, which are both hobbled by very low clock speeds and relatively small L3 cache sizes.

For reasons known only to Intel, they do not have "frequency optimized," lower core count processors in the Xeon E7-4800 v2 Product Family. In fact they have just the opposite situation, since the base and turbo clock speeds drop off pretty dramatically as the core counts go down. The amount of shared L3 cache per physical core also goes down as the core counts get lower with this line of processors. This makes it much less feasible to purposely pick a lower core-count processor than it is with the Xeon E5-2600 v2 Product Family.

Since Microsoft does not care (for licensing purposes) whether you have a fast physical processor core or a slow physical processor core, you are best served from a performance and scalability perspective by getting the best physical processor core you can for a given physical core count processor. But what does this argument look like from a capital cost perspective? After all, we do have a responsibility to make sound business decisions as part of our selection process. There is a seemingly significant cost difference between these three processors, as shown in Table 2.

Model Cores Base Speed Turbo Speed L3 Cache Size Cost
E7-4890 v2 15 2.8GHz 3.4GHz 37.5MB $6,619.00
E7-4880 v2 15 2.5GHz 3.1GHz 37.5MB $5,506.00
E7-4870 v2 15 2.3GHz 2.9GHz 30MB $4,394.00

Table 2: Three Xeon E7 Processor Models Compared

Choosing the slower Xeon E7-4880 v2 processor instead of the E7-4890 v2 processor would save you $4,452.00 in a four-socket server (assuming the server vendor does not take a markup on the processors over Intel’s price). Choosing the even slower Xeon E7-4870 v2 processor instead of the E7-4890 v2 processor would save you $8,900.00 in a four-socket server. That seems like a lot of money, but if you look at the total cost of the server, including software license costs, it is actually pretty insignificant.

A fifteen-core processor in a four-socket server will require 60 total SQL Server 2014 Enterprise Edition core licenses that cost $6,874.00 each, for a total SQL Server license cost of $412,440.00. If you fill all 96 memory slots in this new four socket server with relatively affordable 16GB DDR3 DIMMs , you will spend about $18,432.00 on memory. If you were to get relatively pricey 32GB DIMMs, you would spend about $76,800.00 on 3TB of memory. You are also looking at perhaps $15-20K more in other fixed costs for this four-socket server, for the chassis, power supplies, HBAs, NICs, RAID controllers, OS licenses, etc. Saving $4,452.00-$8,900.00 on a roughly $500K purchase is not going to be significant to most organizations, especially when they understand how much performance and scalability they will be losing for such a small savings.

There is a recent TPC-E benchmark submission for a four-socket IBM System x3850 X6 system that has four Intel Xeon E7-4890 v2 processors that has an actual score of 5576.27 (which is also the highest TPC-E score ever). By doing some simple arithmetic, we can come up with some credible estimated TPC-E scores for the other two lower speed, fifteen-core processors.

I take the average difference in the base clock speed and the turbo clock speed for each processor, and multiply the actual TPC-E score for the E7-4890 v2 by that to come up with an initial estimate. So for example, multiplying 5576.27 times .906 gives a TPC-E estimate of 5052.10 for the E7-4880 v2 processor. Since the L3 cache is the same size between those two processors, we are done with the E7-4880 v2 processor.

We do the same thing for the slower E7-4870 v2 processor, so 5576.27 times .837 gives a TPC-E estimate of 4667.11. Since the shared L3 cache is significantly smaller in the E7-4870 v2 processor, I also subtract another 10% (which is just an educated guess), to come up with a final TPC-E estimate of 4200.40 for the E7-4870 v2 processor.

These simple calculations are only valid since these three processors are all from the same processor family and generation, with the same core count, and all of their other specifications are identical.

Model TPC-E Score Base Speed Turbo Speed L3 Cache/Core
E7-4890 v2 5576.27 100% 100% 2.5MB
E7-4880 v2 5052.10 89.3% 91.8% 2.5MB
E7-4870 v2 4200.40 82.1% 85.3% 2.0MB

Table 3: Estimated TPC-E Scores for Three Xeon E7 Processors

As you can see from this exercise, you are giving up about 10% of your performance and scalability to save $4,452.00 on a roughly $500K investment if you choose the Xeon E7-4870 v2 processor instead of the Xeon E7-4890 v2 processor, meaning you are giving up 10% of your performance to save about 1% of the cost of the system. The picture is even worse if you include the I/O subsystem cost for a system like this.