function microtimeFloat() {
    list($usec,$sec) = explode(" ", microtime());
    return((float)$usec + (float)$sec);
}

1.测试file_put_contents

复制代码 代码如下:
<?php
$userCount = 1000;
$itemCount = 1000;
$file = 'ratings.txt';
file_exists($file) &&unlink($file);

$timeStart = microtimeFloat();
for ($i = 0; $i < $userCount; $i++) {
    $uid =random(32);
    for ($j = 0;$j < $itemCount; $j++) {
       $itemId = mt_rand(1, 300000);
       $rating = $j == 0 ? 1 : mt_rand(1, 100) / 100;
       $line = sprintf("%s,%d,%s\n", $uid, $itemId, $rating);
       file_put_contents($file, $line, FILE_APPEND);
    }
}
$timeEnd = microtimeFloat();
echo sprintf("Spend time: |%s| second(s)\n", $timeEnd -$timeStart);
?>

测试结果:
测试过程中出现了打开文件的错误，而且程序执行完成以后写入的数据不完整，只有999997行，漏了3行。最重要的一点是时间花了307秒多，而用fwrite只花了10秒多的时间，差距还是不小的。

D:\myphp\research>php test2.php
PHP Warning: file_put_contents(ratings.txt): failed to open stream:Permission
denied in D:\myphp\research\test2.php on line 79

Warning: file_put_contents(ratings.txt): failed to open stream:Permission denie
d in D:\myphp\research\test2.php on line 79
Spend time: |307.0586669445|second(s)

...
999994:98xDtLjaeD8MG9ywifegZvRRQzVBZbbw,167670,0.15
999995:98xDtLjaeD8MG9ywifegZvRRQzVBZbbw,234223,0.13
999996:98xDtLjaeD8MG9ywifegZvRRQzVBZbbw,84947,0.79
999997:98xDtLjaeD8MG9ywifegZvRRQzVBZbbw,6489,0.38

2.测试fwrite

复制代码 代码如下:
<?php
$userCount = 1000;
$itemCount = 1000;
$file = 'ratings.txt';
file_exists($file) &&unlink($file);

$fp = @fopen($file, 'ab');
if (!$fp) die("Open $file failed");

$timeStart = microtimeFloat();
for ($i = 0; $i < $userCount; $i++) {
    $uid =random(32);
    for ($j = 0;$j < $itemCount; $j++) {
       $itemId = mt_rand(1, 300000);
       $rating = $j == 0 ? 1 : mt_rand(1, 100) / 100;
       $line = sprintf("%s,%d,%s\n", $uid, $itemId, $rating);
       fwrite($fp, $line);
       $k++;
    }
}
if ($fp) @fclose($fp);
$timeEnd = microtimeFloat();
echo sprintf("Spend time: |%s| second(s)\n", $timeEnd -$timeStart);
?>

测试结果:
写一百万行记录，10秒左右写完，对于PHP来说，速度算不错了。这是在我的个人电脑上面测试的，如果在生产机上测试，可能速度还要快一些。
D:\myphp\research>php test2.php
Spend time: |10.764221191406|second(s)

用fwrite写入的数据是完整的
999997,QOvcZYFJFlFHjiGyGxAc615kOXdX3Yii,246982,0.03
999998,QOvcZYFJFlFHjiGyGxAc615kOXdX3Yii,240160,0.39
999999,QOvcZYFJFlFHjiGyGxAc615kOXdX3Yii,46296,0.61
1000000,QOvcZYFJFlFHjiGyGxAc615kOXdX3Yii,26211,0.14

3.总结
如果要往文件里面写入大量的数据，则推荐用fwrite，不要用file_put_contents。在高并发的请求中也建议用fwrite。