Companion

Default maximum segment size. A segment of this size or larger will never be merged. @see setMaxMergeDocs

Default merge factor, which is how many segments are merged at a time

Default noCFSRatio. If a merge's size is >= 10% of the index, then we disable compound file for it.

Defines the allowed range of log(size) for each level. A level is computed by taking the max segment log size, minus LEVEL_LOG_SPAN, and finding all segments falling within that range.