I know that in general if you optimize an index the document id that a HitCollector would see is not guarenteed to stay the same since any deleted documents would get removed from the index completely and all later documents pushed up to fill in the gaps. I'm wondering though, are the document ids are preserved accross an optimize if there were no deletions (which could be checked with a call to IndexReader.hasDeletions())?
Similarly, if you populate an index using IndexWriter.addIndexes(Directory[]) are the document ids preserved except with offsets added? That is, if you have two indices with 10 documents each (so that each has document ids 0-9) and combine them in this way, does document 0 in the new index correspond to document 0 in the Directory[0] index, ..., document[9] correspond to document 9 in Directory[0], document[10] correspond to document 0 in Directory[1],...,document[17] correspond to document 9 in Directory[1]. I've been creating a prototype of something that for a first pass assumed that documents are preserved as described above, but some of my results are starting to look like that is not the case. Thanks.
