为什么 PHP8 将包含 DDL 语句的事务改为异常抛出？

Question

在 PHP 8.0 以前的版本，包含 DDL 语句的事务只是会触发隐式提交（应该算是 MySQL 的功能，并不是 PHP 的特性），事务无法回滚，并不会抛异常。而8.0版本 commit 时会直接抛异常 There is no active transaction。 8.0 是基于什么考虑抛这个异常出来呢？似乎在 ChangeLog 也没有提到有这个变更。

测试代码如下

$conn = new PDO("mysql:host=127.0.0.1;dbname=test", 'root', '123456');
 $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
 $conn->beginTransaction();
 try {
 $sql = "CREATE TABLE IF NOT EXISTS test (`id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT, `text` varchar(32) NOT NULL DEFAULT '', PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;";
 $conn->exec($sql);
 
 $sql = "INSERT INTO test values(1,'test1')";
 $conn->exec($sql);
 
 $conn->commit();
 } catch (Exception $e) {
 echo $e->getMessage();
 $conn->rollBack();
 }

Answer 1

我近期也在测试php8，也发现了这个变化。

这是由于这个PDO变更导致的
https://github.com/php/php-sr...

Fix inconsistency in PDO transaction state

This addresses an issue introduced by #4996 and reported in
https://bugs.php.net/bug.php?id=80260.

Now that PDO::inTransaction() reports the real transaction state
of the connection, there may be a mismatch with PDOs internal
transaction state (in_tcx). This is compounded by the fact that
MySQL performs implicit commits for DDL queries.

This patch fixes the issue by making beginTransaction/commit/rollBack
work on the real transaction state provided by the driver as well
(or falling back to in_tcx if the driver does not support it).

This does mean that writing something like

$pdo->beginTransaction();
$pdo->exec('CREATE DATABASE ...');
$pdo->rollBack(); // <- illegal

will now result in an error, because the CREATE DATABASE already
committed the transaction. I believe this behavior is both correct
and desired -- otherwise, there is no indication that the code did
not behave correctly and the rollBack() was effectively ignored.
However, this is also a BC break.