When a segment is being merged away, new segments are created. There might me decorated readers for it. There need to be a way to notify decorators that a segment/reader has gone away to allow for cleanup etc.
Proposed api in ZoieIndexReaderDecorator:
void undecorate(ZoieIndexReader reader);
Seems this information is only known by the combination of MergePolicy and the ref counting code. What do you think?