diff --git a/phpBB/phpbb/mention/controller/mention.php b/phpBB/phpbb/mention/controller/mention.php
index a188ea6bf8..d2b43d0914 100644
--- a/phpBB/phpbb/mention/controller/mention.php
+++ b/phpBB/phpbb/mention/controller/mention.php
@@ -44,10 +44,10 @@ class mention
 
 	public function handle()
 	{
-//		if (!$this->request->is_ajax())
-//		{
-//			new RedirectResponse(append_sid($this->phpbb_root_path . 'index.' . $this->php_ext));
-//		}
+		if (!$this->request->is_ajax())
+		{
+			new RedirectResponse(append_sid($this->phpbb_root_path . 'index.' . $this->php_ext));
+		}
 
 		$keyword = $this->request->variable('keyword', '', true);
 		$topic_id = $this->request->variable('topic_id', 0);
diff --git a/phpBB/phpbb/mention/source/base_group.php b/phpBB/phpbb/mention/source/base_group.php
index d7037f77ae..607fb91cc9 100644
--- a/phpBB/phpbb/mention/source/base_group.php
+++ b/phpBB/phpbb/mention/source/base_group.php
@@ -68,14 +68,15 @@ abstract class base_group implements source_interface
 				'FROM'   => [
 					GROUPS_TABLE => 'g',
 				],
-				'LEFT_JOIN'	=> array(
-					array(
-						'FROM'	=> array(USER_GROUP_TABLE => 'ug'),
+				'LEFT_JOIN'	=> [
+					[
+						'FROM'	=> [USER_GROUP_TABLE => 'ug'],
 						'ON'	=> 'ug.group_id = g.group_id AND ug.user_pending = 0 AND ug.user_id = ' . (int) $this->user->data['user_id'],
-					),
-				),
+					],
+				],
 			]);
-			$result = $this->db->sql_query($query);
+			// Cache results for 5 minutes
+			$result = $this->db->sql_query($query, 600);
 
 			$this->groups = [];
 			while ($row = $this->db->sql_fetchrow($result))
@@ -111,8 +112,8 @@ abstract class base_group implements source_interface
 	 */
 	public function get(array &$names, $keyword, $topic_id)
 	{
-		// Grab all group IDs
-		$result = $this->db->sql_query($this->query($keyword, $topic_id));
+		// Grab all group IDs, cache for 5 minutes
+		$result = $this->db->sql_query($this->query($keyword, $topic_id), 300);
 
 		$group_ids = [];
 		while ($row = $this->db->sql_fetchrow($result))
@@ -142,7 +143,5 @@ abstract class base_group implements source_interface
 				'rank'		=> $group_rank['title'],
 			]);
 		}
-
-		return $names;
 	}
 }
diff --git a/phpBB/phpbb/mention/source/base_user.php b/phpBB/phpbb/mention/source/base_user.php
index 7ac830fc6e..8ab1d05df1 100644
--- a/phpBB/phpbb/mention/source/base_user.php
+++ b/phpBB/phpbb/mention/source/base_user.php
@@ -76,10 +76,27 @@ abstract class base_user implements source_interface
 	public function get(array &$names, $keyword, $topic_id)
 	{
 		$keyword = utf8_clean_string($keyword);
-		$result = $this->db->sql_query_limit($this->query($keyword, $topic_id), self::NAMES_BATCH_SIZE);
 
-		while ($row = $this->db->sql_fetchrow($result))
+		// Do not query all possible users (just a moderate amount), cache results for 5 minutes
+		$result = $this->db->sql_query($this->query($keyword, $topic_id), 300);
+
+		$i = 0;
+		while ($i < self::NAMES_BATCH_SIZE)
 		{
+			$row = $this->db->sql_fetchrow($result);
+
+			if (!$row)
+			{
+				break;
+			}
+
+			if (!empty($keyword) && strpos($row['username_clean'], $keyword) !== 0)
+			{
+				continue;
+			}
+
+			$i++;
+
 			$user_rank = $this->user_loader->get_rank($row['user_id'], true);
 			array_push($names, [
 				'name'		=> $row['username'],
@@ -95,7 +112,5 @@ abstract class base_user implements source_interface
 		}
 
 		$this->db->sql_freeresult($result);
-
-		return $names;
 	}
 }
diff --git a/phpBB/phpbb/mention/source/friend.php b/phpBB/phpbb/mention/source/friend.php
index 60e706b458..dfd90a813c 100644
--- a/phpBB/phpbb/mention/source/friend.php
+++ b/phpBB/phpbb/mention/source/friend.php
@@ -33,8 +33,13 @@ class friend extends base_user
 	 */
 	protected function query($keyword, $topic_id)
 	{
+		/*
+		 * For optimization purposes all friends are returned regardless of the keyword
+		 * Names filtering is done on the frontend
+		 * Results will be cached on a per-user basis
+		 */
 		$query = $this->db->sql_build_query('SELECT', [
-			'SELECT'    => 'u.username, u.user_id',
+			'SELECT'    => 'u.username_clean, u.username, u.user_id',
 			'FROM'      => [
 				USERS_TABLE => 'u',
 			],
@@ -45,8 +50,7 @@ class friend extends base_user
 				]
 			],
 			'WHERE'     => 'z.friend = 1 AND z.user_id = ' . (int) $this->user->data['user_id'] . '
-				AND ' . $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER]) . '
-				AND u.username_clean ' . $this->db->sql_like_expression($keyword . $this->db->get_any_char()),
+				AND ' . $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER]),
 			'ORDER_BY'  => 'u.user_lastvisit DESC'
 		]);
 		return $query;
diff --git a/phpBB/phpbb/mention/source/source_interface.php b/phpBB/phpbb/mention/source/source_interface.php
index 43b6106363..7c7da7369f 100644
--- a/phpBB/phpbb/mention/source/source_interface.php
+++ b/phpBB/phpbb/mention/source/source_interface.php
@@ -17,12 +17,11 @@ interface source_interface
 {
 	/**
 	 * Searches database for names to mention
-	 * and returns and array of found items
+	 * and alters the passed array of found items
 	 *
 	 * @param array  $names    Array of already fetched data with names
 	 * @param string $keyword  Search string
 	 * @param int    $topic_id Current topic ID
-	 * @return array Array of names
 	 */
 	public function get(array &$names, $keyword, $topic_id);
 }
diff --git a/phpBB/phpbb/mention/source/team.php b/phpBB/phpbb/mention/source/team.php
index 2cfffd9f82..89c1f4071e 100644
--- a/phpBB/phpbb/mention/source/team.php
+++ b/phpBB/phpbb/mention/source/team.php
@@ -20,16 +20,20 @@ class team extends base_user
 	 */
 	protected function query($keyword, $topic_id)
 	{
+		/*
+		 * For optimization purposes all team members are returned regardless of the keyword
+		 * Names filtering is done on the frontend
+		 * Results will be cached in a single file
+		 */
 		$query = $this->db->sql_build_query('SELECT', [
-			'SELECT'    => 'u.username, u.user_id',
+			'SELECT'    => 'u.username_clean, u.username, u.user_id',
 			'FROM'      => [
 				USERS_TABLE => 'u',
 				USER_GROUP_TABLE => 'ug',
 				TEAMPAGE_TABLE => 't',
 			],
 			'WHERE'     => 'ug.group_id = t.group_id AND ug.user_id = u.user_id AND ug.user_pending = 0
-				AND ' . $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER]) . '
-				AND u.username_clean ' . $this->db->sql_like_expression($keyword . $this->db->get_any_char()),
+				AND ' . $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER]),
 			'ORDER_BY'  => 'u.user_lastvisit DESC'
 		]);
 		return $query;
diff --git a/phpBB/phpbb/mention/source/topic.php b/phpBB/phpbb/mention/source/topic.php
index 688495ddc7..da1d6152d6 100644
--- a/phpBB/phpbb/mention/source/topic.php
+++ b/phpBB/phpbb/mention/source/topic.php
@@ -20,6 +20,11 @@ class topic extends base_user
 	 */
 	protected function query($keyword, $topic_id)
 	{
+		/*
+		 * For optimization purposes all users are returned regardless of the keyword
+		 * Names filtering is done on the frontend
+		 * Results will be cached on a per-topic basis
+		 */
 		$query = $this->db->sql_build_query('SELECT', [
 			'SELECT'    => 'u.username, u.user_id',
 			'FROM'      => [
@@ -32,8 +37,7 @@ class topic extends base_user
 				]
 			],
 			'WHERE'     => 'p.topic_id = ' . $topic_id . '
-				AND ' . $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER]) . '
-				AND u.username_clean ' . $this->db->sql_like_expression($keyword . $this->db->get_any_char()),
+				AND ' . $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER]),
 			'ORDER_BY'  => 'p.post_time DESC'
 		]);
 		return $query;
diff --git a/phpBB/phpbb/mention/source/user.php b/phpBB/phpbb/mention/source/user.php
index 8a03bc41a8..d37ff416c0 100644
--- a/phpBB/phpbb/mention/source/user.php
+++ b/phpBB/phpbb/mention/source/user.php
@@ -20,13 +20,14 @@ class user extends base_user
 	 */
 	protected function query($keyword, $topic_id)
 	{
+		// TODO: think about caching ALL users: 1m users results to ~40MB file
 		$query = $this->db->sql_build_query('SELECT', [
-			'SELECT'    => 'u.username, u.user_id',
+			'SELECT'    => 'u.username_clean, u.username, u.user_id',
 			'FROM'      => [
 				USERS_TABLE => 'u',
 			],
-			'WHERE'     => $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER]) . '
-				AND u.username_clean ' . $this->db->sql_like_expression($keyword . $this->db->get_any_char()),
+			'WHERE'     => $this->db->sql_in_set('u.user_type', [USER_NORMAL, USER_FOUNDER])/* . '
+				AND u.username_clean ' . $this->db->sql_like_expression($keyword . $this->db->get_any_char())*/,
 			'ORDER_BY'  => 'u.user_lastvisit DESC'
 		]);
 		return $query;
diff --git a/phpBB/phpbb/mention/source/usergroup.php b/phpBB/phpbb/mention/source/usergroup.php
index c3b95ffb49..fd1184ff60 100644
--- a/phpBB/phpbb/mention/source/usergroup.php
+++ b/phpBB/phpbb/mention/source/usergroup.php
@@ -31,7 +31,7 @@ class usergroup extends base_group
 					'ON'   => 'g.group_id = ug.group_id'
 				]
 			],
-			'WHERE'     => 'ug.user_id = ' . (int) $this->user->data['user_id'],
+			'WHERE'     => 'ug.user_pending = 0 AND ug.user_id = ' . (int) $this->user->data['user_id'],
 		]);
 		return $query;
 	}