Robert Engels suggested the following idea, here:
http://www.gossamer-threads.com/lists/lucene/java-dev/54217
When merging in the stored fields from a segment, if the field name ->
number mapping is identical then we can simply bulk copy the entire
entry for the document rather than re-interpreting and then re-writing
the actual stored fields.
I've pulled the code from the above thread and got it working on the
current trunk.
Improvement
Closed
Minor
Speedup merging of stored fields when field mapping "matches"
