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Oracle Performance Tuning and Optimization
(Publisher: Macmillan Computer Publishing)
Author(s): Edward Whalen
ISBN: 067230886x
Publication Date: 04/01/96

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Hardware Enhancements

In an OLTP environment, you can make several hardware enhancements to help improve performance. These hardware enhancements can be beneficial in the areas of CPU, I/O, and network, as described in the following sections.

CPU Enhancements

Enhancing the CPUs on your SMP or MPP system can provide instantaneous performance improvements—assuming that you are not I/O bound. Computer manufacturers are continually making improvements to system processors, not only in speed of the CPU itself but in improved CPU caches as well.

If you already have an SMP or MPP machine, enhancing the CPU may be as easy as adding another processor. Before you purchase an additional processor of the same type and speed, however, see whether upgrading to a faster processor can provide more benefit than adding a CPU. For example, upgrading from a 66 MHz processor to a 133 MHz processor may provide more benefit than purchasing an additional 66 MHz CPU—with the added benefit that you now have the option of adding more 133 MHz CPUs. How you enhance your CPU will depend on the upgradability of your computer as well as your budget.

SMP and MPP computers provide scaleable CPU performance enhancements at a fraction of the cost of another computer. When upgrading your processors or adding additional processors, remember that your I/O and memory needs will probably increase along with the CPU performance. Be sure to budget for more memory and disk drives when you add processors.

I/O Enhancements

You can enhance I/O by adding disk drives or purchasing a hardware disk array. OLTP really benefits from disk striping as done by software or hardware disk arrays. If you use Oracle data file striping, the size of the data stripe is so large that there is some dependency on the location of the data being striped. If the data currently being accessed is all in one extent, the effect of Oracle striping is minimal.

By using hardware or software striping with a small stripe size (for example, 16K), you see a natural balancing of I/Os across all the disk drives. This striping provides better load balancing than is possible when you try to balance the load across disks by hand.

Hardware and software disk arrays also have the benefit of optional fault tolerance. As you saw in Chapter 15, “Disk Arrays,” each of the fault tolerant RAID levels has its advantages and disadvantages. You must first choose the correct fault tolerance for your needs and then make sure that you have sufficient I/O capabilities to achieve the required performance level. If you use fault tolerance, you most likely have to increase the number of disk drives in your system.

Another benefit of hardware disk arrays is caching. Most disk arrays on the market today offer some type of write or read/write cache on the controller. The effect of this cache is to improve the speed of writing to the disk and to mask the overhead associated with fault tolerance. If you use RAID-5, you see minimal performance degradation if the controller has a write cache (as long as you don’t exceed the performance of the cache and disks). The write returns to the OS as soon as the data has been written to the write cache.


CAUTION:  It is important to make sure that any controller you use with a write cache is protected against a power failure. Some of the disk array controllers on the market today offer a battery-backed, mirrored memory cache to protect your data. Remember: Once Oracle believes that data has been written to the drive, that data had better be there.

Enhancements to the I/O subsystem almost always help in an OLTP system because most OLTP systems are disk bound. Be sure that you have a sufficient number of disk drives, properly configured. I/O is probably the most important area of OLTP server tuning. Of course, the most effective way to get optimal performance from the system is to have both a well-tuned server and a well-tuned application.


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