Revert "bug #10908 [HttpFoundation] implement session locking for PDO (Tobion)"

This reverts commit 8c71454f47, reversing
changes made to 735e9a4768.

src/Symfony/Component/HttpFoundation/Resources/stubs/SessionHandlerInterface.php

@@ -12,14 +12,6 @@
 /**
  * SessionHandlerInterface for PHP < 5.4
  *
- * The order in which these methods are invoked by PHP are:
- * 1. open [session_start]
- * 2. read
- * 3. gc [optional depending on probability settings: gc_probability / gc_divisor]
- * 4. destroy [optional when session_regenerate_id(true) is used]
- * 5. write [session_write_close] or destroy [session_destroy]
- * 6. close
- *
  * Extensive documentation can be found at php.net, see links:
  *
  * @see http://php.net/sessionhandlerinterface
@@ -27,7 +19,6 @@
  * @see http://php.net/session-set-save-handler
  *
  * @author Drak <drak@zikula.org>
- * @author Tobias Schultze <http://tobion.de>
  */
 interface SessionHandlerInterface
 {
@@ -66,9 +57,6 @@ interface SessionHandlerInterface
     /**
      * Writes the session data to the storage.
      *
-     * Care, the session ID passed to write() can be different from the one previously
-     * received in read() when the session ID changed due to session_regenerate_id().
-     *
      * @see http://php.net/sessionhandlerinterface.write
      *
      * @param string $sessionId Session ID , see http://php.net/function.session-id

src/Symfony/Component/HttpFoundation/Session/Storage/Handler/PdoSessionHandler.php

@@ -12,19 +12,7 @@
 namespace Symfony\Component\HttpFoundation\Session\Storage\Handler;
 
 /**
- * Session handler using a PDO connection to read and write data.
+ * PdoSessionHandler.
- *
- * It works with MySQL, PostgreSQL, Oracle, SQL Server and SQLite and implements
- * locking of sessions to prevent loss of data by concurrent access to the same session.
- * This means requests for the same session will wait until the other one finished.
- * PHPs internal files session handler also works this way.
- *
- * Attention: Since SQLite does not support row level locks but locks the whole database,
- * it means only one session can be accessed at a time. Even different sessions would wait
- * for another to finish. So saving session in SQLite should only be considered for
- * development or prototypes.
- *
- * @see http://php.net/sessionhandlerinterface
  *
  * @author Fabien Potencier <fabien@symfony.com>
  * @author Michael Williams <michael.williams@funsational.com>
@@ -37,11 +25,6 @@ class PdoSessionHandler implements \SessionHandlerInterface
      */
     private $pdo;
 
-    /**
-     * @var string Database driver
-     */
-    private $driver;
-
     /**
      * @var string Table name
      */
@@ -62,50 +45,39 @@ class PdoSessionHandler implements \SessionHandlerInterface
      */
     private $timeCol;
 
-    /**
-     * @var bool Whether a transaction is active
-     */
-    private $inTransaction = false;
-
-    /**
-     * @var bool Whether gc() has been called
-     */
-    private $gcCalled = false;
-
     /**
      * Constructor.
      *
      * List of available options:
-     *  * db_table: The name of the table [default: sessions]
+     *  * db_table: The name of the table [required]
      *  * db_id_col: The column where to store the session id [default: sess_id]
      *  * db_data_col: The column where to store the session data [default: sess_data]
      *  * db_time_col: The column where to store the timestamp [default: sess_time]
      *
-     * @param \PDO  $pdo     A \PDO instance
+     * @param \PDO  $pdo       A \PDO instance
-     * @param array $options An associative array of DB options
+     * @param array $dbOptions An associative array of DB options
      *
-     * @throws \InvalidArgumentException When PDO error mode is not PDO::ERRMODE_EXCEPTION
+     * @throws \InvalidArgumentException When "db_table" option is not provided
      */
-    public function __construct(\PDO $pdo, array $options = array())
+    public function __construct(\PDO $pdo, array $dbOptions = array())
     {
+        if (!array_key_exists('db_table', $dbOptions)) {
+            throw new \InvalidArgumentException('You must provide the "db_table" option for a PdoSessionStorage.');
+        }
         if (\PDO::ERRMODE_EXCEPTION !== $pdo->getAttribute(\PDO::ATTR_ERRMODE)) {
             throw new \InvalidArgumentException(sprintf('"%s" requires PDO error mode attribute be set to throw Exceptions (i.e. $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION))', __CLASS__));
         }
-
         $this->pdo = $pdo;
-        $this->driver = $this->pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);
+        $dbOptions = array_merge(array(
-
-        $options = array_replace(array(
-            'db_table'    => 'sessions',
             'db_id_col'   => 'sess_id',
             'db_data_col' => 'sess_data',
             'db_time_col' => 'sess_time',
-        ), $options);
+        ), $dbOptions);
 
-        $this->table = $options['db_table'];
+        $this->table = $dbOptions['db_table'];
-        $this->idCol = $options['db_id_col'];
+        $this->idCol = $dbOptions['db_id_col'];
-        $this->dataCol = $options['db_data_col'];
+        $this->dataCol = $dbOptions['db_data_col'];
-        $this->timeCol = $options['db_time_col'];
+        $this->timeCol = $dbOptions['db_time_col'];
     }
 
     /**
@@ -113,56 +85,14 @@ class PdoSessionHandler implements \SessionHandlerInterface
      */
     public function open($savePath, $sessionName)
     {
-        $this->gcCalled = false;
-
         return true;
     }
 
     /**
      * {@inheritdoc}
      */
-    public function read($sessionId)
+    public function close()
     {
-        $this->beginTransaction();
-
-        try {
-            $this->lockSession($sessionId);
-
-            // We need to make sure we do not return session data that is already considered garbage according
-            // to the session.gc_maxlifetime setting because gc() is called after read() and only sometimes.
-            $maxlifetime = (int) ini_get('session.gc_maxlifetime');
-
-            $sql = "SELECT $this->dataCol FROM $this->table WHERE $this->idCol = :id AND $this->timeCol > :time";
-
-            $stmt = $this->pdo->prepare($sql);
-            $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
-            $stmt->bindValue(':time', time() - $maxlifetime, \PDO::PARAM_INT);
-            $stmt->execute();
-
-            // We use fetchAll instead of fetchColumn to make sure the DB cursor gets closed
-            $sessionRows = $stmt->fetchAll(\PDO::FETCH_NUM);
-
-            if ($sessionRows) {
-                return base64_decode($sessionRows[0][0]);
-            }
-
-            return '';
-        } catch (\PDOException $e) {
-            $this->rollback();
-
-            throw $e;
-        }
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function gc($maxlifetime)
-    {
-        // We delay gc() to close() so that it is executed outside the transactional and blocking read-write process.
-        // This way, pruning expired sessions does not block them from being started while the current session is used.
-        $this->gcCalled = true;
-
         return true;
     }
 
@@ -179,14 +109,56 @@ class PdoSessionHandler implements \SessionHandlerInterface
             $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
             $stmt->execute();
         } catch (\PDOException $e) {
-            $this->rollback();
+            throw new \RuntimeException(sprintf('PDOException was thrown when trying to delete a session: %s', $e->getMessage()), 0, $e);
-
-            throw $e;
         }
 
         return true;
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function gc($maxlifetime)
+    {
+        // delete the session records that have expired
+        $sql = "DELETE FROM $this->table WHERE $this->timeCol < :time";
+
+        try {
+            $stmt = $this->pdo->prepare($sql);
+            $stmt->bindValue(':time', time() - $maxlifetime, \PDO::PARAM_INT);
+            $stmt->execute();
+        } catch (\PDOException $e) {
+            throw new \RuntimeException(sprintf('PDOException was thrown when trying to delete expired sessions: %s', $e->getMessage()), 0, $e);
+        }
+
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function read($sessionId)
+    {
+        $sql = "SELECT $this->dataCol FROM $this->table WHERE $this->idCol = :id";
+
+        try {
+            $stmt = $this->pdo->prepare($sql);
+            $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
+            $stmt->execute();
+
+            // We use fetchAll instead of fetchColumn to make sure the DB cursor gets closed
+            $sessionRows = $stmt->fetchAll(\PDO::FETCH_NUM);
+
+            if ($sessionRows) {
+                return base64_decode($sessionRows[0][0]);
+            }
+
+            return '';
+        } catch (\PDOException $e) {
+            throw new \RuntimeException(sprintf('PDOException was thrown when trying to read the session data: %s', $e->getMessage()), 0, $e);
+        }
+    }
+
     /**
      * {@inheritdoc}
      */
@@ -195,10 +167,8 @@ class PdoSessionHandler implements \SessionHandlerInterface
         // Session data can contain non binary safe characters so we need to encode it.
         $encoded = base64_encode($data);
 
-        // The session ID can be different from the one previously received in read()
-        // when the session ID changed due to session_regenerate_id(). So we have to
-        // do an insert or update even if we created a row in read() for locking.
         // We use a MERGE SQL query when supported by the database.
+        // Otherwise we have to use a transactional DELETE followed by INSERT to prevent duplicate entries under high concurrency.
 
         try {
             $mergeSql = $this->getMergeSql();
@@ -213,18 +183,15 @@ class PdoSessionHandler implements \SessionHandlerInterface
                 return true;
             }
 
-            $updateStmt = $this->pdo->prepare(
+            $this->pdo->beginTransaction();
-                "UPDATE $this->table SET $this->dataCol = :data, $this->timeCol = :time WHERE $this->idCol = :id"
+
-            );
+            try {
-            $updateStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
+                $deleteStmt = $this->pdo->prepare(
-            $updateStmt->bindParam(':data', $encoded, \PDO::PARAM_STR);
+                    "DELETE FROM $this->table WHERE $this->idCol = :id"
-            $updateStmt->bindValue(':time', time(), \PDO::PARAM_INT);
+                );
-            $updateStmt->execute();
+                $deleteStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
+                $deleteStmt->execute();
 
-            // Since we have a lock on the session, this is safe to do. Otherwise it would be prone to
-            // race conditions in high concurrency. And if it's a regenerated session ID it should be
-            // unique anyway.
-            if (!$updateStmt->rowCount()) {
                 $insertStmt = $this->pdo->prepare(
                     "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time)"
                 );
@@ -232,153 +199,18 @@ class PdoSessionHandler implements \SessionHandlerInterface
                 $insertStmt->bindParam(':data', $encoded, \PDO::PARAM_STR);
                 $insertStmt->bindValue(':time', time(), \PDO::PARAM_INT);
                 $insertStmt->execute();
-            }
-        } catch (\PDOException $e) {
-            $this->rollback();
 
-            throw $e;
+                $this->pdo->commit();
-        }
-
-        return true;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function close()
-    {
-        $this->commit();
-
-        if ($this->gcCalled) {
-            $maxlifetime = (int) ini_get('session.gc_maxlifetime');
-
-            // delete the session records that have expired
-            $sql = "DELETE FROM $this->table WHERE $this->timeCol <= :time";
-
-            $stmt = $this->pdo->prepare($sql);
-            $stmt->bindValue(':time', time() - $maxlifetime, \PDO::PARAM_INT);
-            $stmt->execute();
-        }
-
-        return true;
-    }
-
-    /**
-     * Helper method to begin a transaction.
-     *
-     * Since SQLite does not support row level locks, we have to acquire a reserved lock
-     * on the database immediately. Because of https://bugs.php.net/42766 we have to create
-     * such a transaction manually which also means we cannot use PDO::commit or
-     * PDO::rollback or PDO::inTransaction for SQLite.
-     */
-    private function beginTransaction()
-    {
-        if ($this->inTransaction) {
-            $this->rollback();
-
-            throw new \BadMethodCallException(
-                'Session handler methods have been invoked in wrong sequence. ' .
-                'Expected sequence: open() -> read() -> destroy() / write() -> close()');
-        }
-
-        if ('sqlite' === $this->driver) {
-            $this->pdo->exec('BEGIN IMMEDIATE TRANSACTION');
-        } else {
-            $this->pdo->beginTransaction();
-        }
-        $this->inTransaction = true;
-    }
-
-    /**
-     * Helper method to commit a transaction.
-     */
-    private function commit()
-    {
-        if ($this->inTransaction) {
-            try {
-                // commit read-write transaction which also releases the lock
-                if ('sqlite' === $this->driver) {
-                    $this->pdo->exec('COMMIT');
-                } else {
-                    $this->pdo->commit();
-                }
-                $this->inTransaction = false;
             } catch (\PDOException $e) {
-                $this->rollback();
+                $this->pdo->rollback();
 
                 throw $e;
             }
-        }
+        } catch (\PDOException $e) {
-    }
+            throw new \RuntimeException(sprintf('PDOException was thrown when trying to write the session data: %s', $e->getMessage()), 0, $e);
-
-    /**
-     * Helper method to rollback a transaction.
-     */
-    private function rollback()
-    {
-        // We only need to rollback if we are in a transaction. Otherwise the resulting
-        // error would hide the real problem why rollback was called. We might not be
-        // in a transaction when two callbacks (e.g. destroy and write) are invoked that
-        // both fail.
-        if ($this->inTransaction) {
-            if ('sqlite' === $this->driver) {
-                $this->pdo->exec('ROLLBACK');
-            } else {
-                $this->pdo->rollback();
-            }
-            $this->inTransaction = false;
-        }
-    }
-
-    /**
-     * Exclusively locks the row so other concurrent requests on the same session will block.
-     *
-     * This prevents loss of data by keeping the data consistent between read() and write().
-     * We do not use SELECT FOR UPDATE because it does not lock non-existent rows. And a following
-     * INSERT when not found can result in a deadlock for one connection.
-     *
-     * @param string $sessionId Session ID
-     */
-    private function lockSession($sessionId)
-    {
-        switch ($this->driver) {
-            case 'mysql':
-                // will also lock the row when actually nothing got updated (id = id)
-                $sql = "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time) " .
-                    "ON DUPLICATE KEY UPDATE $this->idCol = $this->idCol";
-                break;
-            case 'oci':
-                // DUAL is Oracle specific dummy table
-                $sql = "MERGE INTO $this->table USING DUAL ON ($this->idCol = :id) " .
-                    "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time) " .
-                    "WHEN MATCHED THEN UPDATE SET $this->idCol = $this->idCol";
-                break;
-            case 'sqlsrv':
-                // MS SQL Server requires MERGE be terminated by semicolon
-                $sql = "MERGE INTO $this->table USING (SELECT 'x' AS dummy) AS src ON ($this->idCol = :id) " .
-                    "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time) " .
-                    "WHEN MATCHED THEN UPDATE SET $this->idCol = $this->idCol;";
-                break;
-            case 'pgsql':
-                // obtain an exclusive transaction level advisory lock
-                $sql = 'SELECT pg_advisory_xact_lock(:lock_id)';
-                $stmt = $this->pdo->prepare($sql);
-                $stmt->bindValue(':lock_id', hexdec(substr($sessionId, 0, 15)), \PDO::PARAM_INT);
-                $stmt->execute();
-
-                return;
-            default:
-                return;
         }
 
-        // We create a DML lock for the session by inserting empty data or updating the row.
+        return true;
-        // This is safer than an application level advisory lock because it also prevents concurrent modification
-        // of the session from other parts of the application.
-        $stmt = $this->pdo->prepare($sql);
-        $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
-        $stmt->bindValue(':data', '', \PDO::PARAM_STR);
-        $stmt->bindValue(':time', time(), \PDO::PARAM_INT);
-        $stmt->execute();
     }
 
     /**
@@ -388,7 +220,9 @@ class PdoSessionHandler implements \SessionHandlerInterface
      */
     private function getMergeSql()
     {
-        switch ($this->driver) {
+        $driver = $this->pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);
+
+        switch ($driver) {
             case 'mysql':
                 return "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time) " .
                     "ON DUPLICATE KEY UPDATE $this->dataCol = VALUES($this->dataCol), $this->timeCol = VALUES($this->timeCol)";
@@ -396,12 +230,12 @@ class PdoSessionHandler implements \SessionHandlerInterface
                 // DUAL is Oracle specific dummy table
                 return "MERGE INTO $this->table USING DUAL ON ($this->idCol = :id) " .
                     "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time) " .
-                    "WHEN MATCHED THEN UPDATE SET $this->dataCol = :data, $this->timeCol = :time";
+                    "WHEN MATCHED THEN UPDATE SET $this->dataCol = :data";
             case 'sqlsrv':
                 // MS SQL Server requires MERGE be terminated by semicolon
                 return "MERGE INTO $this->table USING (SELECT 'x' AS dummy) AS src ON ($this->idCol = :id) " .
                     "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time) " .
-                    "WHEN MATCHED THEN UPDATE SET $this->dataCol = :data, $this->timeCol = :time;";
+                    "WHEN MATCHED THEN UPDATE SET $this->dataCol = :data;";
             case 'sqlite':
                 return "INSERT OR REPLACE INTO $this->table ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time)";
         }

src/Symfony/Component/HttpFoundation/Tests/Session/Storage/Handler/PdoSessionHandlerTest.php

@@ -29,108 +29,74 @@ class PdoSessionHandlerTest extends \PHPUnit_Framework_TestCase
         $this->pdo->exec($sql);
     }
 
-    /**
+    public function testIncompleteOptions()
-     * @expectedException \InvalidArgumentException
+    {
-     */
+        $this->setExpectedException('InvalidArgumentException');
+        $storage = new PdoSessionHandler($this->pdo, array());
+    }
+
     public function testWrongPdoErrMode()
     {
-        $this->pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_SILENT);
+        $pdo = new \PDO("sqlite::memory:");
+        $pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_SILENT);
+        $pdo->exec("CREATE TABLE sessions (sess_id VARCHAR(255) PRIMARY KEY, sess_data TEXT, sess_time INTEGER)");
 
-        $storage = new PdoSessionHandler($this->pdo);
+        $this->setExpectedException('InvalidArgumentException');
+        $storage = new PdoSessionHandler($pdo, array('db_table' => 'sessions'));
     }
 
-    /**
+    public function testWrongTableOptionsWrite()
-     * @expectedException \RuntimeException
-     */
-    public function testInexistentTable()
     {
-        $storage = new PdoSessionHandler($this->pdo, array('db_table' => 'inexistent_table'));
+        $storage = new PdoSessionHandler($this->pdo, array('db_table' => 'bad_name'));
-        $storage->open('', 'sid');
+        $this->setExpectedException('RuntimeException');
-        $storage->read('id');
+        $storage->write('foo', 'bar');
-        $storage->write('id', 'data');
-        $storage->close();
     }
 
-    public function testReadWriteRead()
+    public function testWrongTableOptionsRead()
     {
-        $storage = new PdoSessionHandler($this->pdo);
+        $storage = new PdoSessionHandler($this->pdo, array('db_table' => 'bad_name'));
-        $storage->open('', 'sid');
+        $this->setExpectedException('RuntimeException');
-        $this->assertSame('', $storage->read('id'), 'New session returns empty string data');
+        $storage->read('foo', 'bar');
-        $storage->write('id', 'data');
-        $storage->close();
-
-        $storage->open('', 'sid');
-        $this->assertSame('data', $storage->read('id'), 'Written value can be read back correctly');
-        $storage->close();
     }
 
-    /**
+    public function testWriteRead()
-     * Simulates session_regenerate_id(true) which will require an INSERT or UPDATE (replace)
-     */
-    public function testWriteDifferentSessionIdThanRead()
     {
-        $storage = new PdoSessionHandler($this->pdo);
+        $storage = new PdoSessionHandler($this->pdo, array('db_table' => 'sessions'));
-        $storage->open('', 'sid');
+        $storage->write('foo', 'bar');
-        $storage->read('id');
+        $this->assertEquals('bar', $storage->read('foo'), 'written value can be read back correctly');
-        $storage->destroy('id');
-        $storage->write('new_id', 'data_of_new_session_id');
-        $storage->close();
-
-        $storage->open('', 'sid');
-        $this->assertSame('data_of_new_session_id', $storage->read('new_id'), 'Data of regenerated session id is available');
-        $storage->close();
     }
 
-    /**
+    public function testMultipleInstances()
-     * @expectedException \BadMethodCallException
-     */
-    public function testWrongUsage()
     {
-        $storage = new PdoSessionHandler($this->pdo);
+        $storage1 = new PdoSessionHandler($this->pdo, array('db_table' => 'sessions'));
-        $storage->open('', 'sid');
+        $storage1->write('foo', 'bar');
-        $storage->read('id');
+
-        $storage->read('id');
+        $storage2 = new PdoSessionHandler($this->pdo, array('db_table' => 'sessions'));
+        $this->assertEquals('bar', $storage2->read('foo'), 'values persist between instances');
     }
 
     public function testSessionDestroy()
     {
-        $storage = new PdoSessionHandler($this->pdo);
+        $storage = new PdoSessionHandler($this->pdo, array('db_table' => 'sessions'));
+        $storage->write('foo', 'bar');
+        $this->assertCount(1, $this->pdo->query('SELECT * FROM sessions')->fetchAll());
 
-        $storage->open('', 'sid');
+        $storage->destroy('foo');
-        $storage->read('id');
-        $storage->write('id', 'data');
-        $storage->close();
-        $this->assertEquals(1, $this->pdo->query('SELECT COUNT(*) FROM sessions')->fetchColumn());
 
-        $storage->open('', 'sid');
+        $this->assertCount(0, $this->pdo->query('SELECT * FROM sessions')->fetchAll());
-        $storage->read('id');
-        $storage->destroy('id');
-        $storage->close();
-        $this->assertEquals(0, $this->pdo->query('SELECT COUNT(*) FROM sessions')->fetchColumn());
-
-        $storage->open('', 'sid');
-        $this->assertSame('', $storage->read('id'), 'Destroyed session returns empty string');
-        $storage->close();
     }
 
     public function testSessionGC()
     {
-        $previousLifeTime = ini_set('session.gc_maxlifetime', 0);
+        $storage = new PdoSessionHandler($this->pdo, array('db_table' => 'sessions'));
-        $storage = new PdoSessionHandler($this->pdo);
 
-        $storage->open('', 'sid');
+        $storage->write('foo', 'bar');
-        $storage->read('id');
+        $storage->write('baz', 'bar');
-        $storage->write('id', 'data');
-        $storage->close();
-        $this->assertEquals(1, $this->pdo->query('SELECT COUNT(*) FROM sessions')->fetchColumn());
 
-        $storage->open('', 'sid');
+        $this->assertCount(2, $this->pdo->query('SELECT * FROM sessions')->fetchAll());
-        $this->assertSame('', $storage->read('id'), 'Session already considered garbage, so not returning data even if it is not pruned yet');
-        $storage->gc(0);
-        $storage->close();
-        $this->assertEquals(0, $this->pdo->query('SELECT COUNT(*) FROM sessions')->fetchColumn());
 
-        ini_set('session.gc_maxlifetime', $previousLifeTime);
+        $storage->gc(-1);
+        $this->assertCount(0, $this->pdo->query('SELECT * FROM sessions')->fetchAll());
     }
 
     public function testGetConnection()