func (db *DB) newIterator(seq uint64, ro *opt.ReadOptions) *dbIter {
	rawIter := db.newRawIterator(ro)
	iter := &dbIter{
		cmp:    db.s.cmp.cmp,
		iter:   rawIter,
		seq:    seq,
		strict: db.s.o.GetStrict(opt.StrictIterator) || ro.GetStrict(opt.StrictIterator),
	}
	runtime.SetFinalizer(iter, (*dbIter).Release)
	return iter
}

func (db *DB) newRawIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
	em, fm := db.getMems()
	v := db.s.version()

	ti := v.getIterators(slice, ro)
	n := len(ti) + 2
	i := make([]iterator.Iterator, 0, n)
	i = append(i, em.NewIterator(slice))
	if fm != nil {
		i = append(i, fm.NewIterator(slice))
	}
	i = append(i, ti...)
	strict := db.s.o.GetStrict(opt.StrictIterator) || ro.GetStrict(opt.StrictIterator)
	mi := iterator.NewMergedIterator(i, db.s.icmp, strict)
	mi.SetReleaser(&versionReleaser{v: v})
	return mi
}

func (v *version) getIterators(slice *util.Range, ro *opt.ReadOptions) (its []iterator.Iterator) {
	// Merge all level zero files together since they may overlap
	for _, t := range v.tables[0] {
		it := v.s.tops.newIterator(t, slice, ro)
		its = append(its, it)
	}

	strict := v.s.o.GetStrict(opt.StrictIterator) || ro.GetStrict(opt.StrictIterator)
	for _, tables := range v.tables[1:] {
		if len(tables) == 0 {
			continue
		}

		it := iterator.NewIndexedIterator(tables.newIndexIterator(v.s.tops, v.s.icmp, slice, ro), strict, true)
		its = append(its, it)
	}

	return
}

func (db *DB) newIterator(seq uint64, slice *util.Range, ro *opt.ReadOptions) *dbIter {
	var islice *util.Range
	if slice != nil {
		islice = &util.Range{}
		if slice.Start != nil {
			islice.Start = newIKey(slice.Start, kMaxSeq, tSeek)
		}
		if slice.Limit != nil {
			islice.Limit = newIKey(slice.Limit, kMaxSeq, tSeek)
		}
	}
	rawIter := db.newRawIterator(islice, ro)
	iter := &dbIter{
		icmp:   db.s.icmp,
		iter:   rawIter,
		seq:    seq,
		strict: db.s.o.GetStrict(opt.StrictIterator) || ro.GetStrict(opt.StrictIterator),
		key:    make([]byte, 0),
		value:  make([]byte, 0),
	}
	runtime.SetFinalizer(iter, (*dbIter).Release)
	return iter
}

// Find finds key/value pair whose key is greater than or equal to the
// given key. It returns ErrNotFound if the table doesn't contain
// such pair.
//
// The caller should not modify the contents of the returned slice, but
// it is safe to modify the contents of the argument after Find returns.
func (r *Reader) Find(key []byte, ro *opt.ReadOptions) (rkey, value []byte, err error) {
	if r.err != nil {
		err = r.err
		return
	}

	index := r.indexBlock.newIterator(nil)
	defer index.Release()
	if !index.Seek(key) {
		err = index.Error()
		if err == nil {
			err = ErrNotFound
		}
		return
	}
	dataBH, n := decodeBlockHandle(index.Value())
	if n == 0 {
		err = errors.New("leveldb/table: Reader: invalid table (bad data block handle)")
		return
	}
	if r.filterBlock != nil && !r.filterBlock.contains(dataBH.offset, key) {
		err = ErrNotFound
		return
	}
	data := r.getDataIter(dataBH, ro.GetStrict(opt.StrictBlockChecksum), !ro.GetDontFillCache())
	defer data.Release()
	if !data.Seek(key) {
		err = data.Error()
		if err == nil {
			err = ErrNotFound
		}
		return
	}
	rkey = data.Key()
	value = data.Value()
	return
}

// NewIterator returns an iterator of the table.
//
// The returned iterator is not goroutine-safe and should be released
// when not used.
//
// Also read Iterator documentation of the leveldb/iterator package.
func (r *Reader) NewIterator(ro *opt.ReadOptions) iterator.Iterator {
	if r.err != nil {
		return iterator.NewEmptyIterator(r.err)
	}

	index := &indexIter{
		blockIter:   *r.indexBlock.newIterator(nil),
		tableReader: r,
		checksum:    ro.GetStrict(opt.StrictBlockChecksum),
		fillCache:   !ro.GetDontFillCache(),
	}
	return iterator.NewIndexedIterator(index, r.strictIter || ro.GetStrict(opt.StrictIterator), false)
}