Question

最近，我一直试图弄清楚为什么特定的PHP脚本需要这么长时间。它是一个简单的组权限网格，从每个组的前端获取N个复选框，并相应地更新权限表。简单的东西。

为了最大限度地减少到DB的往返，我只是截断了表并为每个权限重新插入行。这样做，我看到插入步骤的性能非常糟糕。所有内容都包含在事务中，所有查询都使用PDO预处理语句。

数据库本身就是MySQL，所有表都在使用InnoDB引擎。插入的特定表格是SUPER simple，仅包含3列，如下所示：

CREATE TABLE `024_group_privs` (
  `group_priv_id` int(11) NOT NULL AUTO_INCREMENT,
  `group_id` int(11) NOT NULL,
  `activity_id` int(11) NOT NULL,
  PRIMARY KEY (`group_priv_id`),
  UNIQUE KEY `group_id` (`group_id`,`activity_id`),
  KEY `activity_id` (`activity_id`),
  CONSTRAINT `024_group_privs_ibfk_1` FOREIGN KEY (`group_id`) REFERENCES `023_groups` (`group_id`),
  CONSTRAINT `024_group_privs_ibfk_2` FOREIGN KEY (`activity_id`) REFERENCES `031_activities` (`activity_id`)
) ENGINE=InnoDB AUTO_INCREMENT=98 DEFAULT CHARSET=latin1

如您所见，一个基本的多对多映射表。

有问题的PHP代码（使用生成后续结果的测试脚手架）如下：

<?php
try {

    //Connect to database
    $db = new PDO('mysql:host=localhost;dbname=mydatabase;charset=utf8', 'user', 'password');

    //Begin transaction.  If there are any errors; this will ensure we still have
    //  a good set of permissions when rolled back
    $db->beginTransaction();

    //Prepare insert and select statement
    $ins_perm = $db->prepare("INSERT INTO 024_group_privs (group_id, activity_id) VALUES (:group_id, :activity_id)");
    $get_act_id = $db->prepare("SELECT activity_page_key FROM 031_activities WHERE activity_id = :activity_id");

    //Nuke existing permissions list; it will be re-built shortly and is faster than
    //  trying to 'true up' the differences in existing permissions with the new ones.
    $trunc_s_time = microtime(true);
    $db->query("SET FOREIGN_KEY_CHECKS = 0");
    $db->query("TRUNCATE TABLE 024_group_privs");
    $db->query("SET FOREIGN_KEY_CHECKS = 1");
    $trunc_e_time = microtime(true);
    print("Trunc time = " . ($trunc_e_time - $trunc_s_time) . "<br/><br/>");

    $tot_ins_time = 0;
    $tot_sel_time = 0;

    //Get grout names from DB, do not trust POST object.
    $query = "SELECT group_name, group_id FROM 023_groups";
    foreach($db->query($query) as $row) {

        //Get current group and related checkbox array.  The names of these arrays are
        //  populated from the DB when the initial page is rendered.
        $group_name = $row['group_name'];
        $group_id = $row['group_id'];
        $perms = $_POST[$group_name];

        //Rebuild permissions for this group
        foreach($perms as $activity_id) {

            //Testing for select statement timing
            $sel_s_time = microtime(true);
            $get_act_id->bindValue(':activity_id', $activity_id, PDO::PARAM_INT);
            $get_act_id->execute();
            $result = $get_act_id->fetchAll(PDO::FETCH_ASSOC);
            $sel_e_time = microtime(true);
            print("Sel time = " . ($sel_e_time - $sel_s_time) . "<br/>");

            //Insert new permission <-- THIS IS THE SLOW QUERY
            $ins_s_time = microtime(true);
            $ins_perm->bindValue(':group_id', $group_id, PDO::PARAM_INT);
            $ins_perm->bindValue(':activity_id', $activity_id, PDO::PARAM_INT);
            $ins_perm->execute();
            $ins_e_time = microtime(true);

            print("Ins time = " . ($ins_e_time - $ins_s_time) . "<br/><br/>");
            $tot_ins_time += ($ins_e_time - $ins_s_time);
            $tot_sel_time += ($sel_e_time - $sel_s_time);
        }

    }
    print("<br/>Total Sel time = " . $tot_sel_time . "<br/>");
    print("Total Ins time = " . $tot_ins_time . "<br/>");
    print("Total time = " . $tot_ins_time + $tot_sel_time . "<br/>");

    //Commit changes
    $db->commit();

    //Close DB connection
    $db = null;

} catch (Exception $ex) {
    set_mysql_status($sid, "An error occurred while processing your request: " . $ex->getMessage());
    $db->rollBack();
}
?>

我的测试结果如下（为简洁起见缩短）：

Trunc time = 2.1458051204681

Sel time = 0.00010895729064941
Ins time = 1.2832479476929

Sel time = 0.00010108947753906
Ins time = 1.2832760810852

Sel time = 0.00010204315185547
Ins time = 1.2749929428101

Sel time = 0.00011420249938965
Ins time = 5.0466451644897

Sel time = 0.00012516975402832
Ins time = 4.5408680438995

...

Total Sel time = 0.010221719741821
Total Ins time = 168.57392191887

问题：给出了什么？我希望编译后的insert语句执行速度要快得多，特别是对于这样的简单数据，更多的是在select语句的行上。数据很小;每个表少于100行。没有表锁，因为这是我的私有（专用）开发环境，并且盒子本身没有其他任何东西在运行，并且马力足以进行简单的数据库事务。

我的理解/期望：由于准备好的语句和事务“包装器”，数据库往返应该最小化。我唯一的想法是，它是由于桌面上的两个外键，但鉴于数据大小与处理它的机器相比，这将是非常可悲的。也许MySQL正在强制每个插入一个完整的硬盘驱动器写入，但这似乎首先会破坏事务的目的。

我搜索了谷歌和搜索引擎优化，但我发现的大多数问题都集中在循环内准备查询或类似的东西。

最后一点：此代码尚未针对安全性进行优化，旨在测试慢插入。提前感谢您的任何帮助。

Answer 1

启用本机预准备语句：

   array(PDO::ATTR_EMULATE_PREPARES => false)

作为PDO的第4个参数解决了这个问题，为什么在DBA stackexchange上询问更好。

使用PDO准备语句插入时MySQL的糟糕性能

1 个答案: