Mysql分布式事务，前提条件

MySQL中只有当隔离级别设置为Serializable的时候才能使用分布式事务。

执行两个命令确认环境

show variables like 'innodb_support_xa';

show variables like '%tx_iso%';

异常信息

根据官方分布式示例

public function test(){Db::transactionXa(function () {$updateTime = time();Db::connect('cdpf_driver')->table('cdpf_driver_user_login_his')->where(["id" => 3128])->update(["login_time" => $updateTime]);Db::connect('cheduo')->table('users')->where(["id" => 2])->update(["updated_at" => date("Y-m-d H:i:s", $updateTime)]);}, [Db::connect('cdpf_driver'),Db::connect('cheduo')]);
}

如果是同一个服务，执行会出现
异常提示:

SQLSTATE[XAE08]: <>: 1440 XAER_DUPID: The XID already exists

解决办法：

方案一：单独编写，不要用thinkphp封装好的

public function test(){$xid = uniqid('xa');$updateTime = time();// 第一个数据库连接$cdpfDriverXid = "cdpf_driver_{$xid}";$cdpfDriverDb = Db::connect('cdpf_driver');$cdpfDriverConnect = $cdpfDriverDb->connect();// 第二个数据库连接$cheduoXid = "cheduo_{$xid}";$cheduoDb = Db::connect('cheduo');$cheduoConnect = $cheduoDb->connect();try {// 第一个事务开始$cdpfDriverConnect->exec("XA begin '$cdpfDriverXid'");$cdpfDriverDb->table('cdpf_driver_user_login_his')->where(["id" => 3128])->update(["login_time" => $updateTime]);$cdpfDriverConnect->exec("XA END '$cdpfDriverXid'");// 到这里挂起// 第二个事务开始$cheduoConnect->exec("XA begin '$cheduoXid'");$cheduoDb->table('users')->where(["id" => 2])->update(["updated_at" => date("Y-m-d H:i:s", $updateTime)]);$cheduoConnect->exec("XA END '$cheduoXid'");// 到这里挂起// 预执行与提交$cdpfDriverConnect->exec("XA PREPARE '$cdpfDriverXid'");$cdpfDriverConnect->exec("XA COMMIT '$cdpfDriverXid'");$cheduoConnect->exec("XA PREPARE '$cheduoXid'");$cheduoConnect->exec("XA COMMIT '$cheduoXid'");} catch (\Exception $ex) {echo $ex->getMessage();// 注意：其实如果语句本身存在问题，并没有走到 XA END。这里回滚会抛出异常$cdpfDriverConnect->exec("XA ROLLBACK '$cdpfDriverXid'");$cheduoConnect->exec("XA ROLLBACK '$cheduoXid'");}return "success";}

方案二，改动源码

namespace think\db;/*** 数据库连接基础类* @property PDO[] $links* @property PDO   $linkID* @property PDO   $linkRead* @property PDO   $linkWrite*/
abstract class PDOConnection extends Connection
{/*** 执行数据库Xa事务* @access public* @param  callable $callback 数据操作方法回调* @param  array    $dbs      多个查询对象或者连接对象* @return mixed* @throws PDOException* @throws \Exception* @throws \Throwable*/public function transactionXa(callable $callback, array $dbs = []){$xid = uniqid('xa');if (empty($dbs)) {$dbs[] = $this;}foreach ($dbs as $key => $db) {if ($db instanceof BaseQuery) {$db = $db->getConnection();$dbs[$key] = $db;}$db->startTransXa($db->getConfig('hostname').'_'.$db->getConfig('database').'_'.$xid);}try {$result = null;if (is_callable($callback)) {$result = $callback($this);}foreach ($dbs as $db) {$db->prepareXa($db->getConfig('hostname').'_'.$db->getConfig('database').'_'.$xid);}foreach ($dbs as $db) {$db->commitXa($db->getConfig('hostname').'_'.$db->getConfig('database').'_'.$xid);}return $result;} catch (\Exception | \Throwable $e) {foreach ($dbs as $db) {$db->rollbackXa($db->getConfig('hostname').'_'.$db->getConfig('database').'_'.$xid);}throw $e;}}
}

下面来分析原因：
其实从错误提醒这里很好得知
分布式唯一ID已经存在了

跟踪源码

namespace think\db;/*** 数据库连接基础类* @property PDO[] $links* @property PDO   $linkID* @property PDO   $linkRead* @property PDO   $linkWrite*/
abstract class PDOConnection extends Connection
{/*** 执行数据库Xa事务* @access public* @param  callable $callback 数据操作方法回调* @param  array    $dbs      多个查询对象或者连接对象* @return mixed* @throws PDOException* @throws \Exception* @throws \Throwable*/public function transactionXa(callable $callback, array $dbs = []){$xid = uniqid('xa');if (empty($dbs)) {$dbs[] = $this;}foreach ($dbs as $key => $db) {if ($db instanceof BaseQuery) {$db = $db->getConnection();$dbs[$key] = $db;}// 问题就在这里，同一个数据库服务器，一个事务ID还没执行完毕// 又循环生成同样的事务ID，导致异常$db->startTransXa($xid);}try {$result = null;if (is_callable($callback)) {$result = $callback($this);}foreach ($dbs as $db) {$db->prepareXa($xid);}foreach ($dbs as $db) {$db->commitXa($xid);}return $result;} catch (\Exception | \Throwable $e) {foreach ($dbs as $db) {$db->rollbackXa($xid);}throw $e;}}}