Change 307300 had a related patch set uploaded (by Lucie Kaffee):
Add prefix search for the Special:Search integreation

https://gerrit.wikimedia.org/r/307300

I -2'ed the patch because we said it will bring up too many things in general and is a mess for performance reasons. We might say the $term string passed from special search to the AP's search hook should be longer than 5 characters to be considered for not prefixed search. This is an easy fix, but I'd need to know first whether it'd actually make a different performance wise. ( @hoo and @aude )

In T143597#2591181, @Lucie wrote:

I -2'ed the patch because we said it will bring up too many things in general and is a mess for performance reasons. We might say the $term string passed from special search to the AP's search hook should be longer than 5 characters to be considered for not prefixed search. This is an easy fix, but I'd need to know first whether it'd actually make a different performance wise. ( @hoo and @aude )

Yes, prefix search gets better (performance wise) if the prefix is longer.

Change 307300 abandoned by Thiemo Kreuz (WMDE):
Add prefix search for the Special:Search integreation

Reason:
I moved the task T143597 back on the AdvancedSearch board. Given the age of this patch I will close it for now. It can still be found from the task and be used as a template for a later patch.

https://gerrit.wikimedia.org/r/307300