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            file_put_contents($pathname, $message . "\n", FILE_APPEND);

file_put_contents - [internal], line ??
Cake\Log\Engine\FileLog::log() - CORE/src/Log/Engine/FileLog.php, line 140
Cake\Log\Log::write() - CORE/src/Log/Log.php, line 392
Cake\Log\Log::warning() - CORE/src/Log/Log.php, line 477
DebugKit\ToolbarService::isSuspiciouslyProduction() - ROOT/vendor/cakephp/debug_kit/src/ToolbarService.php, line 169
DebugKit\ToolbarService::isEnabled() - ROOT/vendor/cakephp/debug_kit/src/ToolbarService.php, line 105
DebugKit\Plugin::bootstrap() - ROOT/vendor/cakephp/debug_kit/src/Plugin.php, line 48
Cake\Http\BaseApplication::pluginBootstrap() - CORE/src/Http/BaseApplication.php, line 182
Cake\Http\Server::bootstrap() - CORE/src/Http/Server.php, line 111
Cake\Http\Server::run() - CORE/src/Http/Server.php, line 79
[main] - ROOT/webroot/index.php, line 40

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Code Context

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            $this->_File->fwrite($contents) &&
            $this->_File->fflush();

SplFileObject::fwrite() - [internal], line ??
Cake\Cache\Engine\FileEngine::set() - CORE/src/Cache/Engine/FileEngine.php, line 141
Cake\Database\Schema\CachedCollection::describe() - CORE/src/Database/Schema/CachedCollection.php, line 85
Cake\ORM\Table::getSchema() - CORE/src/ORM/Table.php, line 513
Cake\ORM\Query::addDefaultTypes() - CORE/src/ORM/Query.php, line 290
Cake\ORM\Query::__construct() - CORE/src/ORM/Query.php, line 184
Cake\ORM\Table::query() - CORE/src/ORM/Table.php, line 1702
Cake\ORM\Table::find() - CORE/src/ORM/Table.php, line 1263
App\Controller\NewsController::action_() - APP/Controller/NewsController.php, line 6437
App\Controller\NewsController::get_data() - APP/Controller/NewsController.php, line 5701
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5625
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3226
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317

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Code Context

        $success = $this->_File->ftruncate(0) &&
            $this->_File->fwrite($contents) &&
            $this->_File->fflush();

SplFileObject::fwrite() - [internal], line ??
Cake\Cache\Engine\FileEngine::set() - CORE/src/Cache/Engine/FileEngine.php, line 141
Cake\I18n\TranslatorRegistry::get() - CORE/src/I18n/TranslatorRegistry.php, line 206
Cake\I18n\I18n::getTranslator() - CORE/src/I18n/I18n.php, line 148
__ - CORE/src/I18n/functions.php, line 45
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3420
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 164
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73

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Code Context

        $success = $this->_File->ftruncate(0) &&
            $this->_File->fwrite($contents) &&
            $this->_File->fflush();

SplFileObject::fwrite() - [internal], line ??
Cake\Cache\Engine\FileEngine::set() - CORE/src/Cache/Engine/FileEngine.php, line 141
Cake\Database\Schema\CachedCollection::describe() - CORE/src/Database/Schema/CachedCollection.php, line 85
Cake\ORM\Table::getSchema() - CORE/src/ORM/Table.php, line 513
Cake\ORM\Query::addDefaultTypes() - CORE/src/ORM/Query.php, line 290
Cake\ORM\Query::__construct() - CORE/src/ORM/Query.php, line 184
Cake\ORM\Table::query() - CORE/src/ORM/Table.php, line 1702
Cake\ORM\Table::find() - CORE/src/ORM/Table.php, line 1263
App\Controller\NewsController::action_() - APP/Controller/NewsController.php, line 6426
App\Controller\NewsController::get_data() - APP/Controller/NewsController.php, line 5701
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5625
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3436
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317

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Code Context

        $success = $this->_File->ftruncate(0) &&
            $this->_File->fwrite($contents) &&
            $this->_File->fflush();

SplFileObject::fwrite() - [internal], line ??
Cake\Cache\Engine\FileEngine::set() - CORE/src/Cache/Engine/FileEngine.php, line 141
Cake\Cache\Cache::write() - CORE/src/Cache/Cache.php, line 266
App\Controller\NewsController::action_() - APP/Controller/NewsController.php, line 6766
App\Controller\NewsController::get_data() - APP/Controller/NewsController.php, line 5701
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5625
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3634
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 164
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73

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Code Context

                ),
                E_USER_WARNING
            );

Cake\Cache\Cache::write() - CORE/src/Cache/Cache.php, line 275
App\Controller\NewsController::action_() - APP/Controller/NewsController.php, line 6766
App\Controller\NewsController::get_data() - APP/Controller/NewsController.php, line 5701
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5625
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3634
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 164
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157

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Code Context

        $success = $this->_File->ftruncate(0) &&
            $this->_File->fwrite($contents) &&
            $this->_File->fflush();

SplFileObject::fwrite() - [internal], line ??
Cake\Cache\Engine\FileEngine::set() - CORE/src/Cache/Engine/FileEngine.php, line 141
Cake\Cache\Cache::write() - CORE/src/Cache/Cache.php, line 266
App\Controller\NewsController::action_() - APP/Controller/NewsController.php, line 6766
App\Controller\NewsController::get_data() - APP/Controller/NewsController.php, line 5701
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5625
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3663
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 164
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73

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Code Context

                ),
                E_USER_WARNING
            );

Cake\Cache\Cache::write() - CORE/src/Cache/Cache.php, line 275
App\Controller\NewsController::action_() - APP/Controller/NewsController.php, line 6766
App\Controller\NewsController::get_data() - APP/Controller/NewsController.php, line 5701
App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5625
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3663
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 164
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157

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Code Context

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                      $a=unserialize($line2);
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App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5571
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::article_show() - APP/Controller/NewsController.php, line 4290
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3822
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 164
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\RoutingMiddleware::process() - CORE/src/Routing/Middleware/RoutingMiddleware.php, line 161

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Code Context

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                      $a=unserialize($line2);
               }

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App\Controller\NewsController::action_cache() - APP/Controller/NewsController.php, line 5571
App\Controller\NewsController::cache_action() - APP/Controller/NewsController.php, line 5281
App\Controller\NewsController::article_show() - APP/Controller/NewsController.php, line 4310
App\Controller\NewsController::view() - APP/Controller/NewsController.php, line 3822
Cake\Controller\Controller::invokeAction() - CORE/src/Controller/Controller.php, line 539
Cake\Controller\ControllerFactory::handle() - CORE/src/Controller/ControllerFactory.php, line 140
Cake\Controller\ControllerFactory::invoke() - CORE/src/Controller/ControllerFactory.php, line 115
Cake\Http\BaseApplication::handle() - CORE/src/Http/BaseApplication.php, line 317
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 77
Cake\Http\Middleware\CsrfProtectionMiddleware::process() - CORE/src/Http/Middleware/CsrfProtectionMiddleware.php, line 164
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\I18n\Middleware\LocaleSelectorMiddleware::process() - CORE/src/I18n/Middleware/LocaleSelectorMiddleware.php, line 61
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Http\Middleware\BodyParserMiddleware::process() - CORE/src/Http/Middleware/BodyParserMiddleware.php, line 157
Cake\Http\Runner::handle() - CORE/src/Http/Runner.php, line 73
Cake\Routing\Middleware\RoutingMiddleware::process() - CORE/src/Routing/Middleware/RoutingMiddleware.php, line 161

SQLServer中的SELECT会阻塞SELECT吗

数据库操作教程 2022-09-23 16:42:50 转载来源: 网络整理/侵权必删

前言在SQLServer中，我们知道一个SELECT语句执行过程中只会申请一些意向共享锁(IS)与共享锁(S),例如我使用SQLProfile跟踪会话86执行SELECT*FROMdbo.TESTWHEREOBJECT_ID=1这个查询语句，其申请、释放的锁资源的过程如下所示：而且从最常见的锁模式的兼容性表，我们可以看到IS锁与S锁都是兼容的，也就是说SELECT查询是不会阻塞SELECT查询的。现有的授权模式请求的模式ISSUIXSIXX意向共享 (IS)是是是是是否共享 (S)是是是否否否更新 (U)是是否否否否意向排他 (IX)是否否是否否意向排他共享(SIX)是否否否否否排他 (X)否否否否否否但是在某些特殊场景

前言

在SQL Server中，我们知道一个SELECT语句执行过程中只会申请一些意向共享锁(IS) 与共享锁(S), 例如我使用SQL Profile跟踪会话86执行SELECT * FROM dbo.TEST WHERE OBJECT_ID =1 这个查询语句，其申请、释放的锁资源的过程如下所示：

而且从最常见的锁模式的兼容性表，我们可以看到IS锁与S锁都是兼容的，也就是说SELECT查询是不会阻塞SELECT查询的。

现有的授权模式

请求的模式

IS

S

U

IX

SIX

X

意向共享 (IS)

是

是

是

是

是

否

共享 (S)

是

是

是

否

否

否

更新 (U)

是

是

否

否

否

否

意向排他 (IX)

是

否

否

是

否

否

意向排他共享(SIX)

是

否

否

否

否

否

排他 (X)

否

否

否

否

否

否

但是在某些特殊场景。你会看到SELECT语句居然“阻塞”SELECT操作，那么SQL Server中SELECT会真的阻塞SELECT操作吗？我们先构造测试的案例场景，那么先准备测试数据吧

CREATE TABLE TEST (OBJECT_ID INT, NAME VARCHAR(8)); CREATE INDEX PK_TEST ON TEST(OBJECT_ID)   DECLARE @Index INT =0; WHILE @Index < 20BEGIN INSERT INTO TEST SELECT @Index, 'kerry';  SET @Index = @Index +1;END

在会话窗口A中，执行下面SQL语句，模拟一个UPDATE语句正在执行

BEGIN TRANSACTION  UPDATE dbo.TEST SET NAME='Kerry' WHERE OBJECT_ID=1; --ROLLBACK;

会话窗口B中，执行下面的SQL语句

SELECT * FROM dbo.TEST WHERE OBJECT_ID=1

会话窗口C中，执行下面的SQL语句

SELECT * FROM dbo.TEST WHERE OBJECT_ID=1

我实验的场景下，会话窗口A的会话ID为85，会话窗口B的会话ID为90,会话窗口C的会话ID为87，如下所示

如下所示，你会看到SELECT语句“阻塞”了SELECT语句，即会话90“阻塞”了会话87，它们的等待事件都为LCK_M_S,也就是说它们都在等待获取共享锁，也许你会置疑这个SQL是否有问题，那么我们使用SP_WHO来查看，你会发现也是如此，如下所示：

如下所示，我们会发现会话ID为90 、87的会话都在等待类型为RID，Resource为1:24171:1的共享锁

其实应该说，会话87、90都在等待RID对象的共享锁，我们知道共享锁与意向共享锁都是兼容的，所以SELECT是不会阻塞SELECT的，那么又怎么解释这个现象呢？在宋大神的指点下，粗略的翻了Database System Implementaion这本书（很多原理性知识，看起来相当吃力）。里面介绍了在锁表（lock table）以及Element Info、Handling Lock Requests、Handling Unlocks等概念,有一个有意思的图所示，

在锁表（lock table）里，elements info里的锁的申请是在一个类似队列的结构。先进先出机制，所以当会话90先进入队列，它在等待共享锁（S), 会话87也进入队列等待共享锁(S)，而且它在会话90的后面（即会话90这个elements info后面的Next指针指向会话87会话的事务）,由于两个会话都被阻塞，这两个会话的Wait字段都是Yes，由于内部某些机制，会话87显示阻塞它的会话为90（这个是我个人臆测，实际具体原因有待考究），实质阻塞的源头还是会话85. 当会话85释放排它锁（X）后，会话队列根据下面几个原则来处理解锁（Handling Unlocks）：

1： First-come-first-served: Grant the lock request that has been waiting the longest. This strategy guarantees no starvation, the situation where a transaction can wait forever for a lock

先来先服务（队列的原则）：授予锁等待时间最长的锁请求，这种策略保证不会饿死（翻译感觉不贴切），即一个事务不会永远等待锁的情况。

2. Priority to shared locks: First grant all the shared locks waiting. Then,grant one update lock, if there are any waiting. Only grant an exclusive lock if no others are waiting. This strategy can allow starvation, if a transaction is waiting for a U or X lock.

共享锁优先，首先授予所有等待共享锁（S），然后授予其中一个更新锁（U),如果有其它类型等待，只有在没有其它锁等待时，才授予排它锁、这一策略允许等待更新锁或排它锁的事务饿死（结束）

3. Priority to upgrading: If there is a transaction with a U lock waiting to upgrade it to an X lock, grant that first. Otherwise, follow one of the other strategies mentioned.

锁升级优先，如果有一个持有共享锁（U)等待升级Wie排他锁（X),那么先授予它排它锁，否则采用前面已经提到的策略中的一个。

按照这些原则，当会话85释放了排它锁（X)后，调度器（Scheduler）应该会根据先后顺序依次授予会话90、87共享锁（S),两者的阻塞会几乎同时消失。这个可以也可以通过实验进行一个大概的推断，在上面实验中，你可以手工取消90会话的查询操作，然后再查看阻塞情况，就会发现会话87被85阻塞了。这个阻塞的源头就变成了85，而不是90了。

PS:上面是个人结合一些知识和理解，做的一些肤浅的判断与分析，如果不对的地方，敬请指正！

参考资料：

Database System Implementaion

总结

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标签: SELECT SQLServer 中的阻塞

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SQLServer中的SELECT会阻塞SELECT吗

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	现有的授权模式
请求的模式	IS	S	U	IX	SIX	X
意向共享 (IS)	是	是	是	是	是	否
共享 (S)	是	是	是	否	否	否
更新 (U)	是	是	否	否	否	否
意向排他 (IX)	是	否	否	是	否	否
意向排他共享(SIX)	是	否	否	否	否	否
排他 (X)	否	否	否	否	否	否

SQLServer中的SELECT会阻塞SELECT吗

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