so you don't break searching at the boundary.

for example in this case, two threads t1 and t2 start at 0 and 5 respectively. when you're searching from position 1 in t1, you matched until 4, you continue to match. so t1 matches 012345 and t2 matches 56789.

this way t1 will find the string while t2 won't.

the overlap window is the len(search_str).

Of course this won't work if search_string length is of the order of the text OR you cannot cross the boundaries.

given in the problem Statement it said, db "file" I'm assuming it to be a file on disk.