Despite some experimenting, i'm unable to find any relevant effect of

Despite some experimenting, i'm unable to find any relevant effect of
creating an index for the keys table on apropos(1) search times;
apparently, adding that index was premature optimization in the first
place; so, stop adding that index.

Its root gone, the following evil is reduced (/usr/share/man on my notebook)
 - DB build time with -Q goes down by 15%, now at 1/3 of makewhatis
 - DB size with -Q goes down by 35%, now at 3.5x of makewhatis
 - full DB build time goes down by 12%, now at 2.1x of makewhatis
 - full DB size goes down by 42%, now at 11.5x of makewhatis

Optimization found somewhere above the Dasht-e Kavir, the Great Salt
Desert, between Tehran (Iran) and Herat (Afghanistan).  Committing
from Melbourne, Australia.