MDL-66955 messages: Improve speed of message search

The OR conditions in the WHERE clause prevented the query from
effectively filtering the messages related to the user quickly, this
change helps gets around this by allowing the database to limit
the rows in the messages table it needs to scan significantly.

message/classes/api.php

@@ -120,7 +120,18 @@ class api {
         $sql = "SELECT $uniqueidsql AS uniqueid, m.id, m.useridfrom, mcm.userid as useridto, m.subject, m.fullmessage,
                        m.fullmessagehtml, m.fullmessageformat, m.smallmessage, m.conversationid, m.timecreated, 0 as isread,
                        $ufields, mub.id as userfrom_blocked, $ufields2, mub2.id as userto_blocked
-                  FROM {messages} m
+                  FROM (
+                        SELECT m2.id AS id
+                          FROM {messages} m2
+                         WHERE m2.useridfrom = ?
+                         UNION
+                        SELECT m3.id AS id
+                          FROM {message_conversation_members} mcm3
+                    INNER JOIN {messages} m3 ON mcm3.conversationid = m3.conversationid
+                         WHERE mcm3.userid = ?
+                       ) der
+            INNER JOIN {messages} m
+                    ON der.id = m.id
             INNER JOIN {user} u
                     ON u.id = m.useridfrom
             INNER JOIN {message_conversations} mc
@@ -143,7 +154,7 @@ class api {
                    AND " . $DB->sql_like('smallmessage', '?', false) . "
               ORDER BY timecreated DESC";
 
-        $params = array($userid, $userid, $userid, self::MESSAGE_ACTION_DELETED, $userid, $userid,
+        $params = array($userid, $userid, $userid, $userid, $userid, self::MESSAGE_ACTION_DELETED, $userid, $userid,
             self::MESSAGE_CONVERSATION_TYPE_SELF, '%' . $search . '%');
 
         // Convert the messages into searchable contacts with their last message being the message that was searched.