Monday, January 30, 2006

Optimizing Object-oriented PHP

1. Initialise all variables before use.

2. Dereference all global/property variables that are frequently used in a method and put the values in local variables if you plan to access the value more than twice.

3. Try placing frequently used methods in the derived classes.

Warning: as PHP is going through a continuous improvement process, things might change in the future.

More Details

I have found that calling object methods (functions defined in a class) are about twice as slow as a normal function calls. To me that's quite acceptable and comparable to other OOP languages.

Inside a method (the following ratios are approximate only):

1. Incrementing a local variable in a method is the fastest. Nearly the same as calling a local variable in a function.
2. Incrementing a global variable is 2 times slow than a local var.
3. Incrementing a object property (eg. $this->prop++) is 3 times slower than a local variable.
4. Incrementing an undefined local variable is 9-10 times slower than a pre-initialized one.
5. Just declaring a global variable without using it in a function also slows things down (by about the same amount as incrementing a local var). PHP probably does a check to see if the global exists.
6. Method invocation appears to be independent of the number of methods defined in the class because I added 10 more methods to the test class (before and after the test method) with no change in performance.
7. Methods in derived classes run faster than ones defined in the base class.
8. A function call with one parameter and an empty function body takes about the same time as doing 7-8 $localvar++ operations. A similar method call is of course about 15 $localvar++ operations.


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