// This is not actual midkey for this half-file; its just border
// around which we split top and bottom. Have to look in files to find
// actual last and first keys for bottom and top halves. Half-files don't
// have an actual midkey themselves. No midkey is how we indicate file is
// not splittable.
this.midkey = new HStoreKey((HStoreKey)mk);
this.midkey.setHRegionInfo(hri);
// Is it top or bottom half?
this.top = Reference.isTopFileRegion(r);
}