search.htm
URLDataThreshold allows to improve
search performance with DBMode=blob
for the queries returning a small number of results
(typically not more than several hundreds).
If search returns fewer than number documents,
full URL information is not loaded from the bdict
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
the bdict table (from the fast source).
Find the number which is good for your installation experimentally.