为什么这段代码会导致服务器上的高平均负载


Why does this code cause high load average on the server?

当从不太稳定的API获得的值在一定范围内时,下面的代码发送一个msg。

这段代码导致平均负载上升,而不是CPU使用率上升,可能是由于高I/O等待。

CentOS 6.5
Kernel 2.6.32-431.11.2.el6.x86_64
Apache 2.2.15
PHP 5.3.3 (mod_fcgid/2.3.7)
> cat /sys/block/sda/queue/scheduler
noop anticipatory deadline [cfq]

该代码在专用硬件和云上都有相同的问题效果(这两种情况都是KVM/Virtio上的VM)。

怎么做才能避免这段代码*导致处理器在处理新指令之前等待指令完成**?我明白降低超时时间并不能真正解决问题,只能减少它的影响。

*这是我对这段代码导致平均负载上升的理解。

<?php
$min = '1';
$last_min = '1';
if (!empty($_GET['min'])) {
    $min = $_GET['min'];
} else {
    $min = false;
}
$ctx=stream_context_create(array('http'=>
    array(
        'timeout' => 10 // seconds timeout
    )
));
$json = file_get_contents('https://www.domain.com/api/ticker/',false,$ctx);
if (!empty($json )) {
    echo($json);
    if (@file_get_contents('log.txt')) {
        if (quote_changed($json)) {
            file_put_contents('log.txt', $json, FILE_APPEND);
        }
    } else {
            file_put_contents('log.txt', $json);
        }
    $obj = json_decode($json,true);
    $last = $obj['ticker']['last'];
    if (is_numeric($last)) {
        $last = (int)$last;
        $last_min = @file_get_contents('last_min.txt');
        $notified = @file_get_contents('notified.txt');
        if ($notified === false) {
            $notified = 'false';
            #echo "no notify file'n";
        }
        if (($last_min === false) || (($min) && ($last_min <> $min))) {
            $last_min = 1;
            $notified = 'false';
            file_put_contents('last_min.txt', $min);
            #echo "no min file or diff min'n";
        }
        #echo ('notified='.$notified.''n');
        if (($last >= $min) && ($notified=='false')) {
            #$url = ('http://otherdomain.com/nexmo/sendmsg.php' . '?name=blah' . $last);
            #file_get_contents($url);
            #switch to SMS when going abroad and plugin new number when available
            mail("8885551212@mail.net","Blah at".$last,"","From: gaia@domain.com'n");
            file_put_contents('notified.txt', 'true');
            #echo "msg sent'n";
            } elseif (($last < $min) && ($notified=='true')) {
                    file_put_contents('notified.txt', 'false');
                    #echo "not sent'n";
        }           
    }
}
function quote_changed($current) {
    $previous = tailCustom('log.txt');
    #echo ('previous='.$previous);
    if ($previous === (trim($current))) {
        return 0;
    } else {
        return 1; 
    }
}
function tailCustom($filepath, $lines = 1, $adaptive = true) {
        // Open file
        $f = @fopen($filepath, "rb");
        if ($f === false) return false;
        // Sets buffer size
        if (!$adaptive) $buffer = 4096;
        else $buffer = ($lines < 2 ? 64 : ($lines < 10 ? 512 : 4096));
        // Jump to last character
        fseek($f, -1, SEEK_END);
        // Read it and adjust line number if necessary
        // (Otherwise the result would be wrong if file doesn't end with a blank line)
        if (fread($f, 1) != "'n") $lines -= 1;
        // Start reading
        $output = '';
        $chunk = '';
        // While we would like more
        while (ftell($f) > 0 && $lines >= 0) {
            // Figure out how far back we should jump
            $seek = min(ftell($f), $buffer);
            // Do the jump (backwards, relative to where we are)
            fseek($f, -$seek, SEEK_CUR);
            // Read a chunk and prepend it to our output
            $output = ($chunk = fread($f, $seek)) . $output;
            // Jump back to where we started reading
            fseek($f, -mb_strlen($chunk, '8bit'), SEEK_CUR);
            // Decrease our line counter
            $lines -= substr_count($chunk, "'n");
        }
        // While we have too many lines
        // (Because of buffer size we might have read too many)
        while ($lines++ < 0) {
            // Find first newline and remove all text before that
            $output = substr($output, strpos($output, "'n") + 1);
        }
        // Close file and return
        fclose($f);
        return trim($output);
}
?>

将数据移动到数据库中,或者如果这不是一个选项,则将不稳定的文件缓存到本地服务器中,这样您就不必每次都访问外部提供商。

如果这两个都不是选项,在我看来,提供API的人需要提高他们的性能,您可以通过通过Firebug测试每次点击花费多少毫秒来验证这一点。