I've been doing some "final" performance testing of 2.3RC1 and
uncovered a fairly serious bug that adds a large fixed CPU cost when
documents have any term vector enabled fields.
The bug does not affect correctness, just performance.
Basically, for every document, we were calling Arrays.fill(0) on a
large (32 KB) byte array when in fact we only needed to zero a small
part of it. This only happens if term vectors are turned on, and is
especially devastating for small documents.