PHP: Measure size in kilobytes of a object/array?

Question

• What's an appropriate way of measure a PHP objects actual size in bytes/kilobytes?

Reason for asking:
I am utilizing memcached for cache storage in my web application that will be used by non-technical customers. However, since memcached has a maximum size of 1mb , it would be great to have a function set up from the beginning that I can be used to measure size of selected objects/arrays/datasets, to prevent them from growing to big.

Note that I am only planning on using this as a alert/diagnostic tool to keep track of the cache performance and storage possibilities over time. I assume that calculating speed on each memcached set/add call would slow down things a bit.

I am also aware of storing big datasets in memcached takes away the whole idea of storing things in the RAM, and that is exactly why I need to know in beforehand to prevent customers building up to big datasets.

Thanks a lot

Solution

Well, since Memcached doesn't store raw objects (it actually stores the serialiezd version), you can do this:

$serializedFoo = serialize($foo);
if (function_exists('mb_strlen')) {
    $size = mb_strlen($serializedFoo, '8bit');
} else {
    $size = strlen($serializedFoo);
}

Comments

[Industrial]

Hi! That's just what I was about to ask. How does it handle UTF8 and multiple byte characters?

[ircmaxell]

Well, it all depends. If you have mb_string function overloading on, then you have issues. If not, strlen will return the byte length (which is what you want in the first place). If you have mbstring.func_overload on, you can use mb_strlen(serialize($foo), '8bit'); in place of strlen. But note, mb_string must be installed to use it. I'll edit in a more robust version...

[Industrial]

Thanks a lot for your help ircmaxell! Great stuff

[Jan Święcki]

@ircmaxell on line 5 of the script you have one too many paranthesis. (can't edit, because SO says edit must have at least 6 characters).

[Andrei Surdu]

What? Never do that!

[f4der]

It would be a challenge to find a method that is more inefficient than this one..

[Tomer Gal]

Don't you dare doing this