摘要：進(jìn)程切換太多，影響了了效率應(yīng)該是原因之一。當(dāng)時，十萬條記錄，個進(jìn)程插入總時間為單進(jìn)程插入萬條數(shù)據(jù)，耗時秒，相對個進(jìn)程插入萬記錄來說，耗時少些。而單進(jìn)程插入萬條記錄，耗時，相對來說，是挺慢的了。

個人在虛擬機centos7，單核，1G內(nèi)存

/**
 * 模擬并發(fā)請求，10萬次寫入數(shù)據(jù)庫
 * 拆分為10個進(jìn)程，每個進(jìn)程處理一萬條插入
 */

$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;

當(dāng)$total=10000，$num = 10;執(zhí)行結(jié)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
總時間為46.88759994506836秒

當(dāng)$total=10000,$num = 100時，執(zhí)行結(jié)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
總時間為7.413399934768677

當(dāng)$total=10000,$num = 1000時，執(zhí)行結(jié)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
總時間為14.71310019493103，相比100個子進(jìn)程，耗時更長了。進(jìn)程切換太多，影響了了效率應(yīng)該是原因之一。

當(dāng)$total=100000 ,$num=100時，十萬條記錄，100個進(jìn)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
總時間為59.70270013809204

單進(jìn)程插入1萬條數(shù)據(jù)，耗時18秒，相對10個進(jìn)程插入1萬記錄來說，耗時少些。
而單進(jìn)程插入10萬條記錄，耗時187.40066790581，相對來說，是挺慢的了。三分鐘。。。

不過，本人再fork 1000個進(jìn)程，來插入10萬記錄時，成功的情況下36秒左右，也可能會出現(xiàn)錯誤，mysqli_connection返回false，是不是連接數(shù)受限制了？

fork 一萬個子進(jìn)程，插入一百萬數(shù)據(jù)，這時，出現(xiàn)連接錯的情況就很多了。最后耗時360秒，數(shù)據(jù)表中插入了945300條記錄,成功率94.53%。于是查看數(shù)據(jù)庫的相關(guān)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 改為10000，然后重啟mysql
實際MySQL服務(wù)器允許的最大連接數(shù)16384；
結(jié)果然并卵，虛擬機好像掛了了。

并發(fā)量大的時候，問題就出在了連接mysql這里。
可以通過一個連接池來嘗試解決該問題。