One of the bottlenecks I have noticed testing Ocean realtime search is the delete process which involves writing several files for each possibly single delete of a document in SegmentReader. The best way to handle the deletes is too simply keep them in memory without flushing them to disk, saving on writing out an entire BitVector per delete. The deletes are saved in the transaction log which is be replayed on recovery.
I am not sure of the best way to approach this, perhaps it is creating a custom class that inherits from SegmentReader. It could reuse the existing reopen and also provide a way to set the deletedDocs BitVector. Also it would be able to reuse FieldsReader by providing locking around FieldsReader for all SegmentReaders of the segment to use. Otherwise in the current architecture each new SegmentReader opens a new FieldsReader which is non-optimal. The deletes would be saved to disk but instead of per delete, periodically like a checkpoint.
