memory - PHP memory_get_usage

Question

I came across the PHP's memory_get_usage() and memory_get_peak_usage().

The problem is that I found that these two functions do not provide the real memory used by the current script. My test script is:

<?php

echo memory_get_usage();

echo '<br />';

$a = str_repeat('hello', 100000);

echo '<br />';

echo memory_get_usage();

echo '<br />';

echo memory_get_peak_usage();

?>

Which returns:

355120

5355216

5356008

What do you understand from this?

The first value is before executing the str_repeat() so it has to be the value of 0.

The second is after the process and it's OK to have a value greater than 0 but not that big value.

The third is the "peak" value and it's slightly greater than the second as I think it should be the biggest value in a processing microsecond.

So do you think that the real value of the current script's memory consumption should be like this:

memory_usage = the second memory usage - the first memory usage

peak_memory_usage = the third (peak_usage) - the first memory usage

which gives:

1) 5355216 - 355120 = 5000096 bytes

2) 5356008 - 355120 = 5000888 bytes

If this is how it works, I assume that the first 355120 bytes are the whole system allocated memory used by apache and other modules, as the first value never changes when you increase or decrease the number of repeats in the str_repeat(), only the two values after the process increase or decrease but never gets smaller that the first value.

Answer 1

According to the php manual, memory_get_usage returns the amount of memory allocated to php, not necessarily the amount being used.