memory_get_peak_usage() with “real usage”

Question

If the real_usage argument is set to true the PHP DOCS say it will get the real size of memory allocated from system. If it\'s false

Answer 1

Introduction

You should use memory_get_usage(false) because what you want is memory used not memory allocated.

Whats the Difference

Your Google Mail might have allocated 25MB of storage for you but it does not mean that is what you have used at the moment.

This is exactly what the PHP doc was saying

Set this to TRUE to get the real size of memory allocated from system. If not set or FALSE only the memory used by emalloc() is reported.

Both argument would return memory allocated relative to the memory limit but the main difference is:

memory_get_usage(false) give the memory used by emalloc() while memory_get_usage(true) returns milestone which can be demonstration here Memory Mile Store

I want to know how close was the script to hit that limit.

That would take some maths and might only work in loops or specific use cases. Why did i say such ?

Imagine

ini_set('memory_limit', '1M');
$data = str_repeat(' ', 1024 * 1024);

The above script would fail before you even get the chance to start start checking memory.

As far as i know the only way i can check memory used for a variable or specific section of PHP is:

$start_memory = memory_get_usage();
$foo = "Some variable";
echo memory_get_usage() - $start_memory;

See Explanation, but if you are in a loop or recursive function you can use maximum memory usage to estimate safely when memory peek would be reached.

Example

ini_set('memory_limit', '1M');

$memoryAvailable = filter_var(ini_get("memory_limit"), FILTER_SANITIZE_NUMBER_INT);
$memoryAvailable = $memoryAvailable * 1024 * 1024;

$peekPoint = 90; // 90%

$memoryStart = memory_get_peak_usage(false);
$memoryDiff = 0;

// Some stats
$stat = array(
        "HIGHEST_MEMORY" => 0,
        "HIGHEST_DIFF" => 0,
        "PERCENTAGE_BREAK" => 0,
        "AVERAGE" => array(),
        "LOOPS" => 0
);

$data = "";
$i = 0;
while ( true ) {
    $i ++;

    // Get used memory
    $memoryUsed = memory_get_peak_usage(false);

    // Get Diffrence
    $memoryDiff = $memoryUsed - $memoryStart;

    // Start memory Usage again
    $memoryStart = memory_get_peak_usage(false);

    // Gather some stats
    $stat['HIGHEST_MEMORY'] = $memoryUsed > $stat['HIGHEST_MEMORY'] ? $memoryUsed : $stat['HIGHEST_MEMORY'];
    $stat['HIGHEST_DIFF'] = $memoryDiff > $stat['HIGHEST_DIFF'] ? $memoryDiff : $stat['HIGHEST_DIFF'];
    $stat['AVERAGE'][] = $memoryDiff;
    $stat['LOOPS'] ++;
    $percentage = (($memoryUsed + $stat['HIGHEST_DIFF']) / $memoryAvailable) * 100;

    // var_dump($percentage, $memoryDiff);

    // Stop your scipt
    if ($percentage > $peekPoint) {

        print(sprintf("Stoped at: %0.2f", $percentage) . "%\n");
        $stat['AVERAGE'] = array_sum($stat['AVERAGE']) / count($stat['AVERAGE']);
        $stat = array_map(function ($v) {
            return sprintf("%0.2f", $v / (1024 * 1024));
        }, $stat);
        $stat['LOOPS'] = $i;
        $stat['PERCENTAGE_BREAK'] = sprintf("%0.2f", $percentage) . "%";
        echo json_encode($stat, 128);
        break;
    }

    $data .= str_repeat(' ', 1024 * 25); // 1kb every time
}

Output

Stoped at: 95.86%
{
    "HIGHEST_MEMORY": "0.71",
    "HIGHEST_DIFF": "0.24",
    "PERCENTAGE_BREAK": "95.86%",
    "AVERAGE": "0.04",
    "LOOPS": 11
}

Live Demo

This may still fail

It may fail because after if ($percentage > $peekPoint) { this still still add to do additional task with also consumes memory

        print(sprintf("Stoped at: %0.2f", $percentage) . "%\n");
        $stat['AVERAGE'] = array_sum($stat['AVERAGE']) / count($stat['AVERAGE']);
        $stat = array_map(function ($v) {
            return sprintf("%0.2f", $v / (1024 * 1024));
        }, $stat);
        $stat['LOOPS'] = $i;
        $stat['PERCENTAGE_BREAK'] = sprintf("%0.2f", $percentage) . "%";
        echo json_encode($stat, 128);
        break;

If the memory to process this request is grater than the memory available the script would fail.

Conclusion

Its not a perfect solution but check for memory at interval and if its exceed peek (eg 90%) exit instantly and leave the fancy stuff