the book said:
Every so often, the buffer is commited:
A new segment—a supplementary inverted index—is written to disk.
A new commit point is written to disk, which includes the name of the new
The disk is fsync’ed—all writes waiting in the filesystem cache are
flushed to disk, to ensure that they have been physically written.
commited is trigged by flush, right? if so, when call refresh, only create a new segment, right?