Measuring the time of PHP scripts - Using $_SERVER['REQUEST_TIME']

问题

Are this methods a reliable way to measure a script:

$time = ($_SERVER['REQUEST_TIME_FLOAT'] - $_SERVER['REQUEST_TIME']);

or

$time = (microtime(true) - $_SERVER['REQUEST_TIME_FLOAT']);

Which one should be used?

And what's the difference of each one?

They return very different measurements.

回答1:

1. $time = ($_SERVER['REQUEST_TIME_FLOAT'] - $_SERVER['REQUEST_TIME']);

This will never give you execution time of you PHP script. Because both the values are used for storing start of request. The difference is, $_SERVER['REQUEST_TIME_FLOAT'] is more precise and stores time value with microsecond precision, while $_SERVER['REQUEST_TIME'] in seconds.

2. $time = (microtime(true) - $_SERVER['REQUEST_TIME_FLOAT']);

I guess this is what should be used at the end of the PHP script and I think you know why.

Also keep in mind $_SERVER['REQUEST_TIME_FLOAT'] is available since PHP 5.4.0.

来源：https://stackoverflow.com/questions/28703822/measuring-the-time-of-php-scripts-using-serverrequest-time