Question

I just noticed – by calling memory_get_peak_usage() on an ’empty’ php file, using php-fastcgi and NGINX, the result is ~120KB of memory

<?php

    print_r(memory_get_peak_usage());

?>

Does PHP really need that ‘much’ memory for every call, or does that only happen for the first call (initializing something I guess) and then every consecutive call needs less Memory?

I’m asking, because I’m kind of surprised that an empty file already uses up 140KB – guessing that a couple of classes, functions and arrays will push that number up quite fast.

And yeah, I know that this probably counts as premature optimization, but I’m really curious about knowing where those 120KB are coming from, and if there’s a way to minify that cost per call.

Answer 1

The first comment on the php.net docs page states:

If you note the peak memory usage of your script is 7MB don’t immediately worry or exacerbate the worry by doing a superficial calculation to tally how much memory the given page will consume for 1000 visitors, for example. Remember this very important fact: such peak script memory consumption is on the level of microseconds. The only way that particular script will require a dedicated 7000MB of memory, given our example, is if all 1000 visitors visited the page at the very same microsecond.

http://php.net/manual/en/function.memory-get-peak-usage.php

And the default allotment per connection is between 8-16mb, so you’re still way below that.

For what it’s worth, doing the same thing on my server yields 650kb, so you’re already doing better than me 😉