Hi,
I have written a simple test program to see how php allocates memory.
Test code allocates ~10 Meg of RAM in an array within a loop till it
runs out of memory as:
$str = rand(65, 95) . rand(65, 95) . rand(65, 95) . rand(65, 95) .
rand(65, 95);
$aa[] = str_repeat($str, 2000000);
What I don't understand here is, for every 10 Meg memory it allocates,
mem usage goes up about 19 Megs when I look at this via top.
Basically, it allocates from physical memory in the beginning, starts
using swap when it is out of RES/Physical memory, which makes me
assume that garbage collection should kick in for temporary string
creations, and each new allocation increases the allocated memory size
by 19 Megs.
Any idea why this is happening, and why do you think memory allocation
is so expensive in PHP?
Thanks..
Results of TOP:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
21843 apache 17 0 19292 5232 3832 S 0.0 0.5 0:00.04 php
21843 apache 16 0 38824 24m 3908 S 0.0 2.4 0:00.10 php
21843 apache 15 0 58356 43m 3912 S 0.0 4.3 0:00.17 php
21843 apache 16 0 77888 62m 3912 S 0.0 6.2 0:00.22 php
21843 apache 15 0 97420 81m 3912 S 0.0 8.1 0:00.29 php
21843 apache 15 0 114m 100m 3912 S 0.0 9.9 0:00.35 php
Results of free -m:
total used free shared buffers cached
Mem: 1011 138 872 0 2 58
Swap: 2008 388 1619
Mem: 1011 158 852 0 2 58
Swap: 2008 388 1619
Mem: 1011 177 833 0 2 58
Swap: 2008 388 1619
Mem: 1011 196 814 0 2 58
Swap: 2008 388 1619
Mem: 1011 216 795 0 2 58
Swap: 2008 388 1619
Mem: 1011 234 776 0 2 58
Swap: 2008 388 1619
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