How to use each bit of memory sensitively in PHP

Question

Hi all , Can any body give me a a introduction of how to program efficiently minimizing memory usage in PHP program correctly and generate my program results using minimum memory ?

Answer 1

It's difficult to give advice with so little information on what you're trying to do and why memory utilization is a problem. In the common scenarios (web servers that serve many requests), memory is not a limiting factory and it's preferable to serve the requests as fast as possible, even if this means sacrificing memory for speed.

However, the following general guidelines apply:

• unset your variables as soon as you don't need them. In a program that's well written, this, however, won't have a big impact, as variables going out of scope have the same effect.
• In long running scripts, with lot's of variables with circular references, and if using PHP 5.3, trey calling the garbage collector explicitly in certain points.

Answer 2

First of all: Don't try to optimize memory usage by using references. PHP is smart enough not to copy the contents of a variable if you do something like this:

$array = array(1,2,3,4,5,);
$var = $array;

PHP will only copy the contents of the variable when you write to it. Using references all the time because you think they will save you copying the variable content can often fire backwards ;)

But, I think your question is hard to answer, as long as you are more precise.

For example if you are working with files it can be recommendable not always to file_get_contents() the whole file, but use the f(open|...) functions to load only small parts of the file at once or even skip whole chunks.

Or if you are working with strings make use of functions which return a string offset instead of the rest of a string (e.g. strcspn instead of strpbrk) when possible.

Answer 3

Based on how I read your question, I think you may be barking up the wrong tree with PHP. It was never designed for a low memory overhead.

If you just want to be as efficient as possible, then look at the other answers. Remember that every single variable costs a fair bit of memory, so use only what you have to, and let the garbage collector work. Make sure that you only declare variables in a local scope so they can get GC'd when the program leaves that scope. Objects will be more expensive than scalar variables. But the biggest common abuse I see are multiple copies of data. If you have a large array, operate directly on it rather than copying it (It may be less CPU efficient, but it should be more memory efficient).

If you are looking to run it in a low memory environment, I'd suggest finding a different language to use. PHP is nice because it manages everything for you (with respect to variables). But that type coersion and flexibility comes at a price (speed and memory usage). Each variable requires a lot of meta-data stored with it. So an 8 byte int (32 bit) would take 8 bytes to store in C, it will likely take more than 64 bytes in PHP (because of all of the "tracking" information associated with it such as type, name, scoping information, etc). That overhead is normally seen as ok since PHP was not designed for large memory loads. So it's a trade-off. More memory used for easier programming. But if you have tight memory constraints, I'd suggest moving to a different language...