php多进程插入数据(pcntl 学习笔记二)

摘要：进程切换太多，影响了了效率应该是原因之一。当时，十万条记录，个进程插入总时间为单进程插入万条数据，耗时秒，相对个进程插入万记录来说，耗时少些。而单进程插入万条记录，耗时，相对来说，是挺慢的了。

个人在虚拟机centos7，单核，1G内存

/**
 * 模拟并发请求，10万次写入数据库
 * 拆分为10个进程，每个进程处理一万条插入
 */

$total = 10000;
$num   = 10;
$per   = $total/$num;

$sql  = "";
$child = "";

echo "start ".microtime(true).PHP_EOL;
for($i = 1; $i<= $num; $i++)
{
    $pid = pcntl_fork();
    if($pid == -1) {
        die("fork error");
    }
    if($pid > 0) {
        //$id = pcntl_wait($status,WNOHANG);
        $child[] = $pid;
    } else if ($pid == 0) {
        $link  = mysqli_connect("localhost","root","root","yii2advanced");
        $start = ($i-1)*$per + 1;
        $end   = $start + $per;
        for($j = $start; $j< $end; $j++){
            $time = microtime(true);
            $sql = "insert pcntl_test (rank,time) values (".$j.",".$time.")";
            mysqli_query($link,$sql);
        }
        mysqli_close($link);
        $id = getmypid();
        echo "child ".$id." finished ".microtime(true).PHP_EOL;
        exit(0);
    }
}

while(count($child)){
    foreach($child as $k => $pid) {
        $res = pcntl_waitpid($pid, $status, WNOHANG);
        if ( -1 == $res || $res > 0) {
            unset($child[$k]);
        }
    }
}
echo "end ".microtime(true).PHP_EOL;

当$total=10000，$num = 10;执行结果如下:

start 1491903371.5548
child 19860 finished 1491903417.2113
child 19857 finished 1491903417.6909
child 19864 finished 1491903417.7793
child 19855 finished 1491903417.8695
child 19859 finished 1491903417.9162
child 19861 finished 1491903418.0089
child 19856 finished 1491903418.0532
child 19863 finished 1491903418.0842
child 19862 finished 1491903418.1474
child 19858 finished 1491903418.4341
end 1491903418.4424
总时间为46.88759994506836秒

当$total=10000,$num = 100时，执行结果如下：

start 1491904334.1735
child 20085 finished 1491904337.0712
child 20086 finished 1491904337.144
……
child 20262 finished 1491904341.5602
child 20264 finished 1491904341.5803
end 1491904341.5869
总时间为7.413399934768677

当$total=10000,$num = 1000时，执行结果如下：

start 1491904562.0166
child 20282 finished 1491904562.1191
child 20277 finished 1491904562.1268
child 20279 finished 1491904562.1352
...
child 21586 finished 1491904576.6954
child 21582 finished 1491904576.7024
child 21584 finished 1491904576.7226
end 1491904576.7297
总时间为14.71310019493103，相比100个子进程，耗时更长了。进程切换太多，影响了了效率应该是原因之一。

当$total=100000 ,$num=100时，十万条记录，100个进程插入

start 1491905670.2652
child 21647 finished 1491905725.4382
child 21651 finished 1491905725.4595
child 21642 finished 1491905725.5402
....
child 21810 finished 1491905729.7709
child 21812 finished 1491905729.8498
child 21811 finished 1491905729.9612
end 1491905729.9679
总时间为59.70270013809204

单进程插入1万条数据，耗时18秒，相对10个进程插入1万记录来说，耗时少些。
而单进程插入10万条记录，耗时187.40066790581，相对来说，是挺慢的了。三分钟。。。

不过，本人再fork 1000个进程，来插入10万记录时，成功的情况下36秒左右，也可能会出现错误，mysqli_connection返回false，是不是连接数受限制了？

fork 一万个子进程，插入一百万数据，这时，出现连接错的情况就很多了。最后耗时360秒，数据表中插入了945300条记录,成功率94.53%。于是查看数据库的相关配置信息

mysql>  show global status like "%connect%";
+-----------------------------------------------+---------------------+
| Variable_name                                 | Value               |
+-----------------------------------------------+---------------------+
| Aborted_connects                              | 0                   |
| Connection_errors_accept                      | 0                   |
| Connection_errors_internal                    | 0                   |
| Connection_errors_max_connections             | 628                 |
| Connection_errors_peer_address                | 0                   |
| Connection_errors_select                      | 0                   |
| Connection_errors_tcpwrap                     | 0                   |
| Connections                                   | 16519               |
| Locked_connects                               | 0                   |
| Max_used_connections                          | 501                 |
| Max_used_connections_time                     | 2017-04-12 15:19:54 |
| Performance_schema_session_connect_attrs_lost | 0                   |
| Ssl_client_connects                           | 0                   |
| Ssl_connect_renegotiates                      | 0                   |
| Ssl_finished_connects                         | 0                   |
| Threads_connected                             | 4                   |
+-----------------------------------------------+---------------------+


mysql>  show global variables like "%connect%";
+-----------------------------------------------+--------------------+
| Variable_name                                 | Value              |
+-----------------------------------------------+--------------------+
| character_set_connection                      | utf8mb4            |
| collation_connection                          | utf8mb4_general_ci |
| connect_timeout                               | 10                 |
| disconnect_on_expired_password                | ON                 |
| init_connect                                  |                    |
| max_connect_errors                            | 100                |
| max_connections                               | 500                |
| max_user_connections                          | 0                  |
| performance_schema_session_connect_attrs_size | 512                |
+-----------------------------------------------+--------------------+

修改 myqsql 配置文件，/etc/my.cnf
把max_connections 改为10000，然后重启mysql
实际MySQL服务器允许的最大连接数16384；
结果然并卵，虚拟机好像挂了了。

并发量大的时候，问题就出在了连接mysql这里。
可以通过一个连接池来尝试解决该问题。