40 Tips for optimizing your php Code(reinholdweber.com)
reinholdweber.com
40 Tips for optimizing your php Code
http://reinholdweber.com/?p=3
11 comments
These range from sensible to utterly useless [1,2,3].
I'd say forget all of this and focus on being a productive developer, building something people want, and ruthlessly avoiding premature optimization. When your application is slow, measure it to find out why, then fix it, and repeat.
1. Let's take #2, "echo is faster than print" - Seriously, is this what we should be worrying about? I can't detect a difference in PHP 5.2.4 across 100,000 echos/prints, so it must not be very big.
2. ++i vs i++ to squeeze out 1 fewer opcode?
3. Using isset($foo{5}) vs a strlen check? I pity the next programmer who has to read and understand the purpose of this code.
I'd say forget all of this and focus on being a productive developer, building something people want, and ruthlessly avoiding premature optimization. When your application is slow, measure it to find out why, then fix it, and repeat.
1. Let's take #2, "echo is faster than print" - Seriously, is this what we should be worrying about? I can't detect a difference in PHP 5.2.4 across 100,000 echos/prints, so it must not be very big.
2. ++i vs i++ to squeeze out 1 fewer opcode?
3. Using isset($foo{5}) vs a strlen check? I pity the next programmer who has to read and understand the purpose of this code.
> Set the maxvalue for your for-loops before and not in the loop.
What does this mean?
What does this mean?
it means that this:
$maxvalue = 100/10; for($i=0; $i<$maxvalue; $i++){ // Some code }
is much faster than this:
for($i=0; $i<100/10; $i++){ // Some code }
because the value is calculated once instead of ten times.
$maxvalue = 100/10; for($i=0; $i<$maxvalue; $i++){ // Some code }
is much faster than this:
for($i=0; $i<100/10; $i++){ // Some code }
because the value is calculated once instead of ten times.
That's not necessarily true. If the compiler is smart enough it won't recalculate the value of a numeric expression which doesn't contain any variables. On the other hand, dereferencing a variable isn't without cost. Of course, in most cases you'd be dereferencing variables anyway in the test clause, so the original idea, compute loop limits before entering the loop, is correct.:
mbp:~/test doug$ time php -r 'for ($i=1; $i<100000000/10; $i++) {$x++;};'
mbp:~/test doug$ time php -r 'for ($i=1; $i<100000000/10; $i++) {$x++;};'
real 0m5.930s
user 0m5.867s
sys 0m0.026s
mbp:~/test doug$ time php -r '$maxval=100000000/10; for ($i=1; $i<$maxval; $i++) {$x++;};'
real 0m6.999s
user 0m6.907s
sys 0m0.029s
mbp:~/test doug$ time perl -e 'for ($i=1; $i<100000000/10; $i++) {$x++;}'
real 0m2.520s
user 0m2.496s
sys 0m0.010s
mbp:~/test doug$ time perl -e '$maxval=100000000/10; for ($i=1; $i<$maxval; $i++) {$x++;}'
real 0m2.537s
user 0m2.499s
sys 0m0.014s
mbp:~/test doug$ time python maxval1.py
real 0m2.134s
user 0m1.761s
sys 0m0.276s
mbp:~/test doug$ time python maxval2.py
real 0m1.890s
user 0m1.588s
sys 0m0.278s
mbp:~/test doug$ time java maxval1
real 0m0.174s
user 0m0.116s
sys 0m0.040s
mbp:~/test doug$ time java maxval2
real 0m0.531s
user 0m0.125s
sys 0m0.041s
Here is the java code too. First maxval1.java:
public class maxval1 {
static int $i, $x;
public static void main(String args[]) throws Exception {
for ($x=$i=1; $i<100000000/10; $i++) {$x++;}
System.out.println($x);
}
}
public class maxval2 {
static int $a, $i, $x;
public static void main(String args[]) throws Exception {
$a=100000000/10;
for ($x=$i=1; $i<$a; $i++) {$x++;}
System.out.println($x);
}
}
Does anyone have any ideas for what's happening in the Python example? Could you post the Python code?
Sure... here is maxval1.py:
for i in range(1, 100000000/10):
pass
maxval=100000000/10
for i in range(1, maxval):
pass
Oh, of course - range() is evaluated once in either case. It returns an array, which is then stepped through. The time difference must have been just some inaccuracy. I guess 'time' isn't the best command to use to test efficiency ... or maybe try adding another 0?
Oh, thanks. I redid it using xrange instead of range and the numbers went down to an average (over 20 tries) of about 1.36 sec for maxval1 (which computes endpoint within the xrange) and 1.9 sec for maxval2 (which uses variable in xrange.)
Ok. The same comes again at point 15:
> Do not use functions inside of for loop, such as for ($x=0; $x < count($array); $x) The count() function gets called each time.
> Do not use functions inside of for loop, such as for ($x=0; $x < count($array); $x) The count() function gets called each time.
Wow!
Prime2() will calculate the prime numbers 4 times faster then Prime1()? Cool.