pkg/ioutil/pagewriter.go
func NewPageWriter(w io.Writer, pageBytes, pageOffset int) *PageWriter {
	return &PageWriter{
		w:                 w,
		pageOffset:        pageOffset,
		pageBytes:         pageBytes,
		buf:               make([]byte, defaultBufferBytes+pageBytes),
		bufWatermarkBytes: defaultBufferBytes,
	}
}
func NewPageWriter(w io.Writer, pageBytes, pageOffset int) *PageWriter {
	return &PageWriter{
		w:                 w,
		pageOffset:        pageOffset,
		pageBytes:         pageBytes,
		buf:               make([]byte, defaultBufferBytes+pageBytes),
		bufWatermarkBytes: defaultBufferBytes,
	}
}
// NewPageWriter creates a new PageWriter. pageBytes is the number of bytes
// to write per page. pageOffset is the starting offset of io.Writer.