最近，我一直试图找出为什么特定的 PHP 脚本花费这么长时间。它是一个简单的组权限网格，从前端为每个组获取 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与数据库的往返次数，我只是截断了表并为每个权限重新插入行。这样做时，我发现插入步骤的性能绝对糟糕。一切都包含在事务中，所有查询都使用 PDO 准备好的语句。
数据库本身是MySQL，所有表都使用InnoDB引擎。插入的具体表非常简单，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，这是一个基本的多对多映射表。
有问题的 PHP 代码(带有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，已缩短):
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:什么给出了？我希望编译后的插入语句的执行速度会比这快得多，尤其是对于如此简单的数据，更符合 select 语句的思路。数据量很小；每个表少于 100 行。没有表锁，因为这是我的私有(private)(专用)开发环境，并且盒子本身没有任何其他东西在上面运行，并且有足够的马力来执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”，数据库往返次数应该最小化。我唯一的想法是，这是表上两个外键的结果，但考虑到数据大小与处理它的机器相比，这将是相当可悲的。也许 MySQL 会在每次插入时强制写入完整的硬盘驱动器，但这似乎从一开始就违背了事务的目的。
我已经搜索了 Google 和 SO，尽管我发现的大多数问题都集中在循环内准备查询或类似的事情上。
最后一点:此代码尚未针对安全性进行优化，旨在测试缓慢的插入。预先感谢您的任何帮助。
最佳答案
启用 native 准备好的语句:
array(PDO::ATTR_EMULATE_PREPARES => false)
作为 PDO 的第四个参数解决了这个问题，至于为什么它有帮助，最好在 DBA stackexchange 上询问。
关于php - 使用 PDO 预准备语句插入时 MySQL 性能极差，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19573419/