SpirirHost Support Centre: MySQL Reference Manual p.333

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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

Chapter 5: MySQL Optimisation 333 5 MySQL Optimisation Optimisation is a complicated task because it ultimately requires understanding of the whole system. While it may be possible to do some local optimisations with small knowledge of your system or application, the more optimal you want your system to become the more you will have to know about it. This chapter will try to explain and give some examples of dierent ways to optimise MySQL. Remember, however, that there are always some (increasingly harder) additional ways to make the system even faster. 5.1 Optimisation Overview The most important part for getting a system fast is of course the basic design. You also need to know what kinds of things your system will be doing, and what your bottlenecks are. The most common bottlenecks are: Disk seeks. It takes time for the disk to nd a piece of data. With modern disks in 1999, the mean time for this is usually lower than 10ms, so we can in theory do about 100 seeks a second. This time improves slowly with new disks and is very hard to optimise for a single table. The way to optimise this is to spread the data on more than one disk. Disk reading/writing. When the disk is at the correct position we need to read the data. With modern disks in 1999, one disk delivers something like 10-20MB/s. This is easier to optimise than seeks because you can read in parallel from multiple disks. CPU cycles. When we have the data in main memory (or if it already were there) we need to process it to get to our result. Having small tables compared to the memory is the most common limiting factor. But then, with small tables speed is usually not the problem. Memory bandwidth. When the CPU needs more data than can t in the CPU cache the main memory bandwidth becomes a bottleneck. This is an uncommon bottleneck for most systems, but one should be aware of it. 5.1.1 MySQL Design Limitations/Tradeos When using the MyISAM table handler, MySQL uses extremely fast table locking (multiple readers / single writers). The biggest problem with this table type is a if you have a mix of a steady stream of updates and slow selects on the same table. If this is a problem with some tables, you can use another table type for these. See Chapter 7 [Table types], page 494. MySQL can work with both transactional and not transactional tables. To be able to work smoothly with not transactional tables (which can't rollback if something goes wrong), MySQL has the following rules:

MySQL Reference Manual

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