URLDataThreshold allows to improve
search performance with
for the queries returning a small number of results
(typically not more than several hundreds).
If search returns fewer than
full URL information is not loaded from the
table and the
url table is used instead.
In other words, URLDataThreshold switches from "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
bdict table (from the fast source).
Find the number which is good for your installation experimentally.