We have made several improvements to the performance of @mentions in large instances, over a couple of versions:
Mentions Plugin 2.1.7
- Don't search if the search string is the same as the last search
- Wait up to 1s for the user to type extra characters, or search every 3 characters (this prevents searches being run on every character while the user is still typing)
- Stop searching if 0 matches are returned on a search string, unless the string no longer contains the previous string (ie stop searching if we have found no results and the user keeps typing)
Mentions Plugin 2.1.8
- All of the above fixes
- If three searches are submitted but the server has not yet returned any results, do not submit new searches until the server responds. This can stop too many searches being run against an instance which is having performance problems.