Interface defining whether or not an object can be cached against a
LeafReader
Objects that depend only on segment-immutable structures such as Points or postings lists
can just return
true from
isCacheable(LeafReaderContext)
Objects that depend on doc values should return
DocValues.isCacheable(LeafReaderContext, String...), which
will check to see if the doc values fields have been updated. Updated doc values fields are not suitable
for cacheing.
Objects that are not segment-immutable, such as those that rely on global statistics or scores,
should return
false