Index: includes/database/database.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/database/database.inc,v
retrieving revision 1.2
diff -u -p -r1.2 database.inc
--- includes/database/database.inc	31 Aug 2008 09:12:35 -0000	1.2
+++ includes/database/database.inc	31 Aug 2008 15:10:29 -0000
@@ -666,6 +666,13 @@ abstract class Database {
   static protected $databaseInfo = NULL;
 
   /**
+   * A list of key/target credentials to simply ignore.
+   * 
+   * @var array
+   */
+  static protected $ignoreTargets = array();
+  
+  /**
    * The key of the currently active database connection.
    *
    * @var string
@@ -695,6 +702,10 @@ abstract class Database {
    *   The corresponding connection object.
    */
   final public static function getConnection($key = 'default', $target = 'default') {
+    if (!empty(self::$ignoreTargets[$key][$target])) {
+      $target = 'default';
+    }
+
     if (!isset(self::$connections[$key][$target])) {
       self::openConnection($key, $target);
     }
@@ -771,6 +782,24 @@ abstract class Database {
 
     self::$databaseInfo = $databaseInfo;
   }
+  
+  /**
+   * Add database connection info for a given key/target.
+   *
+   * If the given key/target pair already exists, this method will be ignored.
+   * 
+   * @param $key
+   *   The database key.
+   * @param $target
+   *   The database target name.
+   * @param $info
+   *   The database connection information, as it would be defined in settings.php.
+   */
+  public static function addConnectionInfo($key, $target, $info) {
+    if (empty(self::$databaseInfo[$key][$target])) {
+      self::$databaseInfo[$key][$target] = $info;
+    }
+  }
 
   /**
    * Gets information on the specified database connection.
@@ -843,6 +872,24 @@ abstract class Database {
       throw $e;
     }
   }
+  
+  /**
+   * Instruct the system to temporarily ignore a given key/target.
+   * 
+   * At times we need to temporarily disable slave queries.  To do so,
+   * call this method with the database key and the target to disable.
+   * That database key will then always fall back to 'default' for that
+   * key, even if it's defined.
+   *
+   * @param $key
+   *   The database connection key.
+   * @param $target
+   *   The target of the specified key to ignore.
+   */
+  public static function ignoreTarget($key, $target) {
+    self::$ignoreTargets[$key][$target] = TRUE;
+  }
+  
 }
 
 /**
Index: modules/simpletest/tests/database_test.test
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/tests/database_test.test,v
retrieving revision 1.1
diff -u -p -r1.1 database_test.test
--- modules/simpletest/tests/database_test.test	31 Aug 2008 11:43:41 -0000	1.1
+++ modules/simpletest/tests/database_test.test	31 Aug 2008 15:10:29 -0000
@@ -104,7 +104,59 @@ class DatabaseTestCase extends DrupalWeb
       ':priority' => 3,
     ));
   }
+}
+
+/**
+ * Test fetch actions, part 1.
+ * 
+ * We get timeout errors if we try to run too many tests at once.
+ */
+class DatabaseConnectionTestCase extends DatabaseTestCase {
+  
+  function getInfo() {
+    return array(
+      'name' => t('Connection tests'),
+      'description' => t('Tests of the core database system.'),
+      'group' => t('Database'),
+    );
+  }
+
+  /**
+   * Test that connections return appropriate connection objects.
+   */
+  function testConnectionRouting() {
+
+    // Clone the master credentials to a slave connection.
+    // Note this will result in two independent connection objects that happen
+    // to point to the same place.
+    $connection_info = Database::getConnectionInfo();
+    Database::addConnectionInfo('default', 'slave', $connection_info['default']['default']);
+    
+    $db1 = Database::getConnection('default', 'default');
+    $db2 = Database::getConnection('default', 'slave');
+    
+    $this->assertFalse($db1 === $db2, t('Both targets refer to the same connection.'));
+  }
+  
+  /**
+   * Test that connections return appropriate connection objects.
+   */
+  function testConnectionRoutingOverride() {
 
+    // Clone the master credentials to a slave connection.
+    // Note this will result in two independent connection objects that happen
+    // to point to the same place.
+    $connection_info = Database::getConnectionInfo('default');
+    Database::addConnectionInfo('default', 'slave', $connection_info['default']);
+    
+    Database::ignoreTarget('default', 'slave');
+    
+    $db1 = Database::getConnection('default', 'default');
+    $db2 = Database::getConnection('default', 'slave');
+    
+    $this->assertTrue($db1 === $db2, t('Both targets refer to the same connection.'));
+  }
+  
 }
 
 /**