Java has both int (32 bit) and long (64 bit) types. What did you refer to as 'native'?

Lucene, the popular core search library, has always used int as internal document IDs. As a result, the number of documents in one Lucene index is limited to 2 billions (Java int are signed). It's even worse if there are many deleted docs in the index as they are are just marked as deleted and consume up IDs. There are a number of reasons why no one is keen on moving internal docIDs to long, and performance is one of them.