18     Performance

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Performance, particularly on busy sites, can be critical - after all, if you can speed up your code by 10%, that decreases your hardware load by 10%, saving you the need to upgrade. There are a number of ways you can improve the performance of your scripts, and we will be covering as many as have space for. We will also be dispelling various myths about optimisation, and hopefully by the end of this chapter you will be confidently about to re-write fundamentally flawed algorithms, tune implementations of good algorithms, make your MySQL queries fly, and more.

Before we begin, I would like to make it quite clear that optimisation is the process of improving performance of your code, whether to use less space or run faster - it is usually a trade-off. Optimised code is not necessarily "perfect code", it is just better than unoptimised code.

Furthermore, there is rarely if ever such a thing as "too fast". In my spare time, I have been working on my own pet project: a gigantic online PHP strategy game. Actions occur at round end, which is triggered by a cron job every ten minutes. With a thousand dummy users in the system, round end takes over seven seconds, during which database writes are locked so that people cannot make changes. In the past I have spent hours and hours just to cut one part of that round end from 0.002 seconds to 0.001 seconds per player - it might not sound like a lot, but as far as I am concerned every single second counts. If you have tried out half of the recommendations here and find you have reduced the run-time for a script from four seconds down to one second, don't stop there - go for the fastest code you can get.

Topics covered in this chapter are:

• Increasing performance by optimising your scripts

• Increasing performance by optimising your SQL

• Increasing performance by optimising your server

• Caching PHP scripts

• PHP the CGI vs. PHP the Apache module

Chapter contents

18.1. Optimising your code

18.1.1. Write your code sensibly
18.1.2. Use your tools wisely
18.1.3. Avoid function for maximum performance
18.1.4. Use the Zend Optimizer
18.1.5. Use a PHP code cache
18.1.6. Read the manual carefully
18.1.7. Get your loops right first
18.1.8. Pre-increment where possible
18.1.9. Don't think that using references will lower your RAM usage
18.1.10. Be wary of garbage collection, part 1
18.1.11. Be wary of garbage collection, part 2
18.1.12. Listen to all errors, big and small
18.1.13. Keep up to date
18.1.14. Cache array data
18.1.15. Compress your output
18.1.16. Don't use CGI
18.1.17. Don't use dl()
18.1.18. Debug your code
18.1.19. Cache your pages
18.1.20. Use persistent connections
18.1.21. Take advantage of new features
18.1.22. Compile right
18.1.23. Ignore the myths
18.1.24. Avoid mod_access if you can
18.1.25. Don't fret about Apache 2.0

18.2. Optimising your SQL

18.2.1. Prioritise your data
18.2.2. Optimise your tables
18.2.3. Select as little data as possible
18.2.4. Use shorter queries where possible
18.2.5. Use the EXPLAIN statement
18.2.6. Change your hardware
18.2.7. Choose your data types carefully
18.2.8. Size vs. Speed
18.2.9. Declare fields NOT NULL
18.2.10. Load data intelligently
18.2.11. Consider splitting off variable-length fields
18.2.12. Be wary of locks
18.2.13. Consider switching OS
18.2.14. Spot slow queries
18.2.15. Perform joins carefully
18.2.16. Index your data
18.2.17. Make sure your indexes are being used
18.2.18. Normalisation
18.2.19. Upgrade MySQL
18.2.20. Increase your buffers
18.2.21. Keep tabs on your server
18.2.22. Lock your tables when appropriate
18.2.23. Don't rely on automatic type conversion
18.2.24. Benchmark, benchmark, benchmark!
18.2.25. Know MySQL's strengths

18.3. Server
18.4. PHP Accelerators
18.5. Caching PHP
18.6. PHP as a CGI or a module?
18.7. Size of scripts
18.8. Summary
18.9. Exercises
18.10. Further reading
18.11. Next chapter