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追踪php代码性能瓶颈
2013年09月02日 php 暂无评论 ⁄ 被围观 6,583 view+

写了一段很简单的代码示例,却发现运行起来速度很慢,出现性能问题的代码量并不大,排除了IO问题以后,写了一段测试代码,果然问题很快重现。

<?php
$y="1800";
$x = array();
for($j=0;$j<2000;$j++){
    $x[]= "{$j}";
}

for($i=0;$i<30000;$i++){
    if(in_array($y,$x)){
        continue;
    }
}
?>

[root@xp trace]# time php test.php
real 0m4.116s
user 0m4.070s
sys 0m0.028s

可以看出时间耗掉了4秒,下面用strace跟踪没拿到什么有效信息。

[root@xp trace]# strace -ttt -o log.txt php test.php
[root@xp trace]# more log.txt

只看到这两次系统调用之间的延时非常大,却并不知道干了什么?一筹莫展了,幸好,Linux下的调试利器除了strace还有ltrace(当然还有dtrace,ptrace)。

引用:strace用来 跟踪一个进程的系统调用或信号产生的情况,而 ltrace用来 跟踪进程调用库函数的情况(via IBM developerworks)。

[root@xp trace]# ltrace -c php test.php

我们看到库函数strtol的调用非常之频繁,太夸张了,然后我又查了一下这个库函数,简单的说就是把字符串转换成长整形,可以猜测PHP引擎已经检测到这是一个字符串型的数字,所以期望将他们转换成长整型来比较,这个转换过程中消耗了太多时间,我们再次执行:

[root@xp trace]# ltrace -e "strtol" php test.php
(0, 0, 0xec4b00, -1, 0x1f25bc2)                                                        = 0x32dd221160
strtol(0x1c9f9d0, 0, 10, 0, 0x7fffe64537f0)                                            = 8
strtol(0x1c9f9b0, 0, 10, 0x7fffe6453880, 0x7fffe64537f0)                               = 30719
strtol(0x1c9f9d0, 0, 10, 0x32ddb8ee88, 0x32ddb8d580)                                   = -9
strtol(0x1c9f070, 0, 10, 371, 0x10119a0)                                               = 0
strtol(0x1c9ea90, 0, 10, 370, 0x10119a0)                                               = 0
strtol(0x1c9e580, 0, 10, 81, 0x1010c60)                                                = 1
strtol(0x1c9fae0, 0, 10, 82, 0x1010c60)                                                = 0
strtol(0x1ca0cf0, 0, 10, 26, 0x1010c60)                                                = 0
strtol(0x1c9f7a0, 0, 10, 408, 0x1010c60)                                               = 0
strtol(0x1c9e6d0, 0, 10, 432, 0x1010c60)                                               = 0
strtol(0xcea563, 0, 10, 433, 0x1010c60)                                                = 0
strtol(0xcea563, 0, 0, 440, 0x1010c60)                                                 = 0
strtol(0x1c9f8f0, 0, 0, 72, 0x1010c60)                                                 = -1
strtol(0xcea563, 0, 10, 298, 0x1010c60)                                                = 0
strtol(0x1c9ee50, 0, 10, 5, 0x1010c60)                                                 = 1
strtol(0x1c9fb80, 0, 10, 83, 0x1010c60)                                                = 1
strtol(0x1c9fc30, 0, 0, 88, 0x1010c60)                                                 = 1024
strtol(0x1c9fce0, 0, 10, 96, 0x1010c60)                                                = 0
strtol(0x1c9fd90, 0, 10, 97, 0x1010c60)                                                = 0
strtol(0x1c9f330, 0, 10, 98, 0x1010c60)                                                = 1
strtol(0x1c9e4d0, 0, 10, 461, 0x1010c60)                                               = 0
strtol(0x1ca05a0, 0, 10, 0, 0x1010c60)                                                 = 0
strtol(0x1ca0650, 0, 10, 1, 0x1010c60)                                                 = 0
strtol(0x1ca0700, 0, 10, 2, 0x1010c60)                                                 = 0
strtol(0x1c9ec70, 0, 0, 8, 0x1010c60)                                                  = 0
strtol(0x1ca03c0, 0, 10, 411, 0x1010c60)                                               = 1
strtol(0x1ca0260, 0, 10, 409, 0x1010c60)                                               = 0
strtol(0x1ca0310, 0, 10, 410, 0x1010c60)                                               = 0
strtol(0x1ca0460, 0, 10, 412, 0x1010c60)                                               = 1
strtol(0x1c9f130, 0, 10, 3, 0x1010c60)                                                 = 0
strtol(0x1c9f1d0, 0, 10, 24, 0x1010c60)                                                = 0
strtol(0x1c9e9f0, 0, 10, 369, 0x10119a0)                                               = 1
strtol(0x1c9feb0, 0, 10, 25, 0x1010c60)                                                = 0
strtol(0x1c9f3d0, 0, 10, 80, 0x1010c60)                                                = 0
strtol(0x1c9ebd0, 0, 10, 413, 0x1010c60)                                               = 1
strtol(0x1c9efe0, 0, 0, 48, 0x1010c60)                                                 = 17
strtol(0x1c9f850, 0, 10, 0, 0)                                                         = 0
strtol(0x1ca0d90, 0, 10, 457, 0x1010c60)                                               = 1
strtol(0x1ca0e40, 0, 0, 160, 0x1010c60)                                                = 1000
strtol(0x1ca0500, 0, 0, 432, 0x1010ec0)                                                = 1000
strtol(0xd214c5, 0, 0, 520, 0x1010c60)                                                 = 64
strtol(0xd37961, 0, 0, 584, 0x1010c60)                                                 = 1000
strtol(0x1ca1250, 0, 10, 560, 0x1010c60)                                               = 1
strtol(0x1c9f990, 0, 0, 0, 0)                                                          = 512
strtol(0x1c9eb30, 0, 10, 0, 0)                                                         = 14
strtol(0x1ca0f80, 0, 10, 459, 0x1010c60)                                               = 1
strtol(0x1ca1030, 0, 10, 512, 0x1010c60)                                               = 0
strtol(0xcea563, 0, 10, 460, 0x1010c60)                                                = 0
strtol(0xd37a32, 0, 0, 24, 0x100ec20)                                                  = 16
strtol(0xd37a49, 0, 0, 32, 0x100ec20)                                                  = 120
strtol(0xd37a7c, 0, 0, 544, 0x1010c60)                                                 = 300
strtol(0xcea563, 0, 10, 513, 0x1010c60)                                                = 0
strtol(0x1c9ef30, 0, 10, 0, 0)                                                         = 30711
strtol(0x1c9f700, 0, 10, 0, 0x1011d80)                                                 = 1
(0x32dd221160, 0, 0, 0x32dd221160, 0)                                                  = 531783
(0, 0, 0, 15, 0x42622d0)                                                               = 0x32dd221160
(0x32dd221160, 0, 0, 0x32dd221160, 0)                                                  = 531720
(0, 0, 0, 11, 0x7f9fa7b51b80)                                                          = 0x32dd221160
(0x32dd221160, 0, 0, 0x32dd221160, 0)                                                  = 531719
(0, 0, 0, 6, 0x9275f60)                                                                = 0x32dd221160
(0x32dd221160, 0, 0, 0x32dd221160, 0)                                                  = 531897
(0, 0, 0, 9, 0x7f9fa74b8338)                                                           = 0x32dd221160
(0x32dd221160, 0, 0, 0x32dd221160, 0)                                                  = 531901
(0, 0, 0, 3, 0x7f9fa72a8340)                                                           = 0x32dd221160
(0x32dd221160, 0, 0, 0x32dd221160, 0)                                                  = 532944
(0, 0, 0, 3, 0x7f9fa70641d0)                                                           = 0x32dd221160
(0x32dd221160, 0, 0, 0x32dd221160, 0)                                                  = 525536
(0, 0, 0, 3, 0x7f9fa6e5c680)                                                           = 0x32dd221160
.....

知道了症结所在,我们解决的办法就很多了,最简单的就是为in_array加第三个参数为true,即变为严格比较,同时还要比较类型,这样避免了PHP自作聪明的转换类型,跑起来果然快多了。

[root@xp trace]# time php test.php
real	0m0.988s
user	0m0.959s
sys	0m0.024s

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