FieldsIndexWriter

Efficient index format for block-based Codecs.

For each block of compressed stored fields, this stores the first document of the block and the start pointer of the block in a DirectMonotonicWriter. At read time, the docID is binary-searched in the DirectMonotonicReader that records doc IDS, and the returned index is used to look up the start pointer in the DirectMonotonicReader that records start pointers.