diff --git a/application/controllers/system/extensions/CLI_Manager.php b/application/controllers/system/extensions/CLI_Manager.php
index ed8a5f7a5..110fad9e8 100644
--- a/application/controllers/system/extensions/CLI_Manager.php
+++ b/application/controllers/system/extensions/CLI_Manager.php
@@ -28,9 +28,10 @@ class CLI_Manager extends CLI_Controller
 	 * die Commandline ohne Upload durchzufuehren.
 	 * @param $extensioName string Name der Extension
 	 * @param $filename Url Encoded Pfad zum tgz File der Extension
+	 * @param $perform_sql boolean ob die SQL Befehle ausgeführt werden
 	 */
-	public function uploadExtension($extensionName = null, $filename = null)
+	public function uploadExtension($extensionName = null, $filename = null, $perform_sql = true)
 	{
-		$this->extensionslib->installExtension($extensionName, urldecode($filename));
+		$this->extensionslib->installExtension($extensionName, urldecode($filename), $perform_sql);
 	}
 }
diff --git a/application/controllers/system/extensions/Manager.php b/application/controllers/system/extensions/Manager.php
index aa4e76e9c..429c967ae 100644
--- a/application/controllers/system/extensions/Manager.php
+++ b/application/controllers/system/extensions/Manager.php
@@ -87,9 +87,13 @@ class Manager extends Auth_Controller
 	 * die Commandline ohne Upload durchzufuehren.
 	 * @param $extensioName string Name der Extension
 	 * @param $filename Url Encoded Pfad zum tgz File der Extension
+	 * @param $perform_sql boolean ob die SQL Befehle ausgeführt werden
 	 */
-	public function uploadExtension($extensionName = null, $filename = null)
+	public function uploadExtension($extensionName = null, $filename = null, $perform_sql = true)
 	{
-		$this->extensionslib->installExtension($extensionName, urldecode($filename));
+		$perform_sql = $this->input->post('databasechange');
+		$perform_sql = isset($perform_sql) ? false : true;
+
+		$this->extensionslib->installExtension($extensionName, urldecode($filename), $perform_sql);
 	}
 }
diff --git a/application/libraries/ExtensionsLib.php b/application/libraries/ExtensionsLib.php
index cec40a753..6598ec2e8 100644
--- a/application/libraries/ExtensionsLib.php
+++ b/application/libraries/ExtensionsLib.php
@@ -64,7 +64,7 @@ class ExtensionsLib
 	 * @param $extensionName string Name of Extension (optional)
 	 * @param $filename Path to tgz Extension File (optional)
 	 */
-	public function installExtension($extensionName = null, $filename = null)
+	public function installExtension($extensionName = null, $filename = null, $perform_sql = true)
 	{
 		$extensionDB = null; // contains data from DB about an extension
 		$extensionJson = null; // contains the extension.json data
@@ -114,7 +114,7 @@ class ExtensionsLib
 
 				$this->_installExtension($extensionJson); // records extension data in DB
 
-				if (!$this->_errorOccurred) // if no error occurred
+				if (!$this->_errorOccurred && $perform_sql === true) // if no error occurred
 				{
 					// Loads and executes neede SQL scripts
 					$this->_loadSQLs(
@@ -173,6 +173,9 @@ class ExtensionsLib
 		$result = $this->_ci->ExtensionsModel->load($extensionId);
 		if (hasData($result)) // if something was found
 		{
+			$extensionServer = $result->retval[0]->server_kurzbz;
+			if ($extensionServer !== SERVER_NAME)
+				return false;
 			$extensionName = $result->retval[0]->name; // extension name
 			$this->_delSoftLinks($extensionName); // not to be checked, could fail if the extension is disabled
 			// remove the extension from the extensions installation directory
@@ -180,10 +183,9 @@ class ExtensionsLib
 
 			// Select all the version of this extension
 			$this->_ci->ExtensionsModel->addSelect('extension_id');
-			$result = $this->_ci->ExtensionsModel->loadWhere(array('name' => $extensionName));
+			$result = $this->_ci->ExtensionsModel->loadWhere(array('name' => $extensionName, 'server_kurzbz' => SERVER_NAME));
 			if (hasData($result)) // if something was found
 			{
-				$extsArray = array();
 				foreach ($result->retval as $key => $extension) // loops on them
 				{
 					// Remove them all
@@ -328,7 +330,7 @@ class ExtensionsLib
 		// Loads the last version of the previous installation of this extension
 		$this->_ci->ExtensionsModel->addOrder('version', 'DESC');
 		$this->_ci->ExtensionsModel->addLimit(1);
-		$result = $this->_ci->ExtensionsModel->loadWhere(array('name' => $extensionName));
+		$result = $this->_ci->ExtensionsModel->loadWhere(array('name' => $extensionName, 'server_kurzbz' => SERVER_NAME));
 		if (isError($result))
 		{
 			$this->_errorOccurred = true;
@@ -550,7 +552,8 @@ class ExtensionsLib
 				'license' => isset($extensionJson->license) ? $extensionJson->license : null,
 				'url' => isset($extensionJson->url) ? $extensionJson->url : null,
 				'core_version' => $extensionJson->core_version,
-				'dependencies' => isset($extensionJson->dependencies) ? $extensionJson->dependencies : null
+				'dependencies' => isset($extensionJson->dependencies) ? $extensionJson->dependencies : null,
+				'server_kurzbz' => SERVER_NAME,
 			)
 		);
 		if (isSuccess($result))
@@ -738,11 +741,18 @@ class ExtensionsLib
 						mkdir($extensionPath.$targetDirectory);
 					}
 
-					// Create the symlink
-					$_addSoftLinks = symlink(
-						$extensionPath.$targetDirectory,
-						$rootPath.$targetDirectory.'/'.ExtensionsLib::EXTENSIONS_DIR_NAME.'/'.$extensionName
-					);
+					if (!file_exists($rootPath.$targetDirectory.'/'.ExtensionsLib::EXTENSIONS_DIR_NAME.'/'.$extensionName))
+					{
+						// Create the symlink
+						$_addSoftLinks = symlink(
+							$extensionPath.$targetDirectory,
+							$rootPath.$targetDirectory.'/'.ExtensionsLib::EXTENSIONS_DIR_NAME.'/'.$extensionName
+						);
+					}else
+					{
+						$_addSoftLinks = true;
+					}
+
 					if (!$_addSoftLinks)
 					{
 						log_message('error', 'Failed to create Symlink to '.$extensionPath.$targetDirectory);
diff --git a/application/models/system/Extensions_model.php b/application/models/system/Extensions_model.php
index 8898ebd50..1beef4d8b 100644
--- a/application/models/system/Extensions_model.php
+++ b/application/models/system/Extensions_model.php
@@ -31,7 +31,7 @@ class Extensions_model extends DB_Model
 	 */
 	public function getInstalledExtensions()
 	{
-		$query = 'SELECT extension_id, e1.name, e1.version, description, license, url, core_version, dependencies, enabled
+		$query = 'SELECT extension_id, e1.name, e1.version, description, license, url, core_version, dependencies, enabled, e1.server_kurzbz
 					FROM system.tbl_extensions e1
 			  INNER JOIN (
 				  SELECT name, MAX(version) AS version
diff --git a/application/views/system/extensions/manager.php b/application/views/system/extensions/manager.php
index 6c48bc80a..01111f295 100644
--- a/application/views/system/extensions/manager.php
+++ b/application/views/system/extensions/manager.php
@@ -108,6 +108,7 @@
 							<th>URL</th>
 							<th>Minimum required Core version</th>
 							<th>Dependes on (extensions)</th>
+							<th>Server</th>
 							<th>Enabled</th>
 							<th>&nbsp;</th>
 						</tr>
@@ -124,6 +125,7 @@
 								<td>%s</td>
 								<td>%s</td>
 								<td>%s</td>
+								<td>%s</td>
 								<td>
 									<input type="checkbox" class="chkbox" name="%s" %s>
 								</td>
@@ -143,6 +145,7 @@
 									$extension->url,
 									$extension->core_version,
 									count($extension->dependencies) == 0 ? 'None' : json_encode($extension->dependencies),
+									$extension->server_kurzbz,
 									$extension->extension_id,
 									$extension->enabled === true ? 'checked' : '',
 									$extension->extension_id
@@ -160,7 +163,9 @@
 
 		<?php echo form_open_multipart(current_url().'/uploadExtension'); ?>
 			<input type="file" name="extension" />
-			<input type="submit" value="Install/Update extension" />
+			<input type="submit" value="Install/Update extension" /> <br/>
+			<input type="checkbox" class="checkbox" id="databasechange" name="databasechange"/>
+			<label for="databasechange">Don´t perform SQL</label>
 		</form>
 
 	</body>
diff --git a/system/dbupdate_3.3.php b/system/dbupdate_3.3.php
index e658d7a97..0bcff4928 100644
--- a/system/dbupdate_3.3.php
+++ b/system/dbupdate_3.3.php
@@ -956,13 +956,39 @@ if ($result = @$db->db_query("SELECT conname FROM pg_constraint WHERE conname =
 // UNIQUE INDEX uidx_extensions_name_version
 if ($result = $db->db_query("SELECT 0 FROM pg_class WHERE relname = 'uidx_extensions_name_version'"))
 {
-	if ($db->db_num_rows($result) == 0)
+	if ($db->db_num_rows($result) == 1)
 	{
-		$qry = 'CREATE UNIQUE INDEX uidx_extensions_name_version ON system.tbl_extensions USING btree (name, version);';
+		$qry = 'DROP INDEX system.uidx_extensions_name_version';
 		if (!$db->db_query($qry))
 			echo '<strong>uidx_extensions_name_version '.$db->db_last_error().'</strong><br>';
 		else
-			echo '<br>Created unique uidx_extensions_name_version';
+			echo '<br>Dropped unique uidx_extensions_name_version';
+	}
+}
+
+// stud_selfservice boolean fuer public.tbl_vorlage
+if(!@$db->db_query("SELECT server_kurzbz FROM system.tbl_extensions LIMIT 1"))
+{
+	$qry = "ALTER TABLE system.tbl_extensions ADD COLUMN server_kurzbz varchar(64);
+			ALTER TABLE system.tbl_extensions ADD CONSTRAINT fk_extensios_server_kurzbz FOREIGN KEY (server_kurzbz) REFERENCES system.tbl_server(server_kurzbz) ON UPDATE CASCADE ON DELETE RESTRICT;";
+
+	if(!$db->db_query($qry))
+		echo '<strong>App: '.$db->db_last_error().'</strong><br>';
+	else
+		echo '<br>Neue Spalte server_kurzbz in system.tbl_extensions hinzugefügt';
+}
+
+
+// UNIQUE INDEX uidx_extensions_name_version_server
+if ($result = $db->db_query("SELECT 0 FROM pg_class WHERE relname = 'uidx_extensions_name_version_server'"))
+{
+	if ($db->db_num_rows($result) == 0)
+	{
+		$qry = 'CREATE UNIQUE INDEX uidx_extensions_name_version_server ON system.tbl_extensions USING btree (name, version, server_kurzbz);';
+		if (!$db->db_query($qry))
+			echo '<strong>uidx_extensions_name_version_server '.$db->db_last_error().'</strong><br>';
+		else
+			echo '<br>Created unique uidx_extensions_name_version_server';
 	}
 }