This command allows to improve search performance with DBMode=blob for the queries
returning a small number of results (not more than several hundreds).
If search returns less than "num" documents,
full URL information is not loaded from the "bdict" table
and the "url" table is used instead. In other words,
this command switches between "loading a huge amount of URL
data from the fast source" to "loading a small amount of URL data
from the slow source".
The default value is 0, which means always read URL data from
the "bdict" table (from the fast source).
Find the number which is good for your installation experimentally.