Upgrade lucene from 2.3.2 to 3.1.0

[Zhang, Lisheng]

We plan to upgrade lucene from 2.3.2 to 3.1.0, from reading "Lucene In Action" 
I learned
that we should "warm up" IndexSearcher and donot expect initial a few queries 
to be fast.
 
But due to our special app we cannot "warm up" (each query has to use a new 
IndexSearcher),
in lucene 2.3.2 this seems OK, Should we encounter obvious performance decrease 
in 3.1.0 
if keeping this way?
 
Thanks very much for helps, Lisheng