=== modified file 'includes/database/database.inc'
--- includes/database/database.inc	2009-12-04 16:31:04 +0000
+++ includes/database/database.inc	2009-12-10 05:50:02 +0000
@@ -832,17 +832,9 @@ abstract class DatabaseConnection extend
   /**
    * Returns a new DatabaseTransaction object on this connection.
    *
-   * @param $required
-   *   If executing an operation that absolutely must use transactions, specify
-   *   TRUE for this parameter. If the connection does not support transactions,
-   *   this method will throw an exception and the operation will not be possible.
    * @see DatabaseTransaction
    */
-  public function startTransaction($required = FALSE) {
-    if ($required && !$this->supportsTransactions()) {
-      throw new TransactionsNotSupportedException();
-    }
-
+  public function startTransaction() {
     if (empty($this->transactionClass)) {
       $this->transactionClass = 'DatabaseTransaction_' . $this->driver();
       if (!class_exists($this->transactionClass)) {
@@ -1575,16 +1567,6 @@ abstract class Database {
 }
 
 /**
- * Exception to mark databases that do not support transations.
- *
- * This exception will be thrown when a transaction is started that does not
- * allow for the "silent fallback" of no transaction and the database connection
- * in use does not support transactions. The calling code must then take
- * appropriate action.
- */
-class TransactionsNotSupportedException extends Exception { }
-
-/**
  * Exception to throw when popTransaction() is called when no transaction is active.
  */
 class NoActiveTransactionException extends Exception { }

=== modified file 'includes/database/mysql/database.inc'
--- includes/database/mysql/database.inc	2009-10-18 07:35:39 +0000
+++ includes/database/mysql/database.inc	2009-12-10 05:50:02 +0000
@@ -14,8 +14,8 @@
 class DatabaseConnection_mysql extends DatabaseConnection {
 
   public function __construct(array $connection_options = array()) {
-    // This driver defaults to non transaction support.
-    $this->transactionSupport = !empty($connection_options['transactions']);
+    // This driver defaults to transaction support, except if explicitly passed FALSE.
+    $this->transactionSupport = !isset($connection_options['transactions']) || ($connection_options['transactions'] !== FALSE);
 
     // MySQL never supports transactional DDL.
     $this->transactionalDDLSupport = FALSE;

=== modified file 'modules/simpletest/tests/database_test.test'
--- modules/simpletest/tests/database_test.test	2009-12-09 19:01:14 +0000
+++ modules/simpletest/tests/database_test.test	2009-12-10 05:50:14 +0000
@@ -2851,49 +2851,6 @@ class DatabaseTransactionTestCase extend
   }
 
   /**
-   * Test that a database that claims to support transactions will return a transaction object.
-   *
-   * If the active connection does not support transactions, this test does nothing.
-   */
-  function testTransactionsSupported() {
-    try {
-      $connection = Database::getConnection();
-      if ($connection->supportsTransactions()) {
-
-        // Start a "required" transaction. This should fail if we do
-        // this on a database that does not actually support transactions.
-        $txn = db_transaction(TRUE);
-      }
-      $this->pass('Transaction started successfully.');
-    }
-    catch (TransactionsNotSupportedException $e) {
-      $this->fail("Exception thrown when it shouldn't have been.");
-    }
-  }
-
-  /**
-   * Test that a database that doesn't support transactions fails correctly.
-   *
-   * If the active connection supports transactions, this test does nothing.
-   */
-  function testTransactionsNotSupported() {
-    try {
-      $connection = Database::getConnection();
-      if (!$connection->supportsTransactions()) {
-
-        // Start a "required" transaction. This should fail if we do this
-        // on a database that does not actually support transactions, and
-        // the current database does claim to NOT support transactions.
-        $txn = db_transaction(TRUE);
-        $this->fail('No transaction failure registered.');
-      }
-    }
-    catch (TransactionsNotSupportedException $e) {
-      $this->pass('Exception thrown for unsupported transactions.');
-    }
-  }
-
-  /**
    * Test transaction rollback on a database that supports transactions.
    *
    * If the active connection does not support transactions, this test does nothing.