// NewIterator returns an iterator for the snapshot of the uderlying DB.
// The returned iterator is not goroutine-safe, but it is safe to use
// multiple iterators concurrently, with each in a dedicated goroutine.
// It is also safe to use an iterator concurrently with modifying its
// underlying DB. The resultant key/value pairs are guaranteed to be
// consistent.
//
// Slice allows slicing the iterator to only contains keys in the given
// range. A nil Range.Start is treated as a key before all keys in the
// DB. And a nil Range.Limit is treated as a key after all keys in
// the DB.
//
// The iterator must be released after use, by calling Release method.
// Releasing the snapshot doesn't mean releasing the iterator too, the
// iterator would be still valid until released.
//
// Also read Iterator documentation of the leveldb/iterator package.
func (snap *Snapshot) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
if err := snap.db.ok(); err != nil {
return iterator.NewEmptyIterator(err)
}
snap.mu.Lock()
defer snap.mu.Unlock()
if snap.released {
return iterator.NewEmptyIterator(ErrSnapshotReleased)
}
// Since iterator already hold version ref, it doesn't need to
// hold snapshot ref.
return snap.db.newIterator(snap.elem.seq, slice, ro)
}
// Creates an iterator from the given table.
func (t *tOps) newIterator(f *tFile, slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
ch, err := t.open(f)
if err != nil {
return iterator.NewEmptyIterator(err)
}
iter := ch.Value().(*table.Reader).NewIterator(slice, ro)
iter.SetReleaser(ch)
return iter
}
// NewIterator returns an iterator for the latest snapshot of the
// uderlying DB.
// The returned iterator is not goroutine-safe, but it is safe to use
// multiple iterators concurrently, with each in a dedicated goroutine.
// It is also safe to use an iterator concurrently with modifying its
// underlying DB. The resultant key/value pairs are guaranteed to be
// consistent.
//
// Slice allows slicing the iterator to only contains keys in the given
// range. A nil Range.Start is treated as a key before all keys in the
// DB. And a nil Range.Limit is treated as a key after all keys in
// the DB.
//
// The iterator must be released after use, by calling Release method.
//
// Also read Iterator documentation of the leveldb/iterator package.
func (db *DB) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
if err := db.ok(); err != nil {
return iterator.NewEmptyIterator(err)
}
se := db.acquireSnapshot()
defer db.releaseSnapshot(se)
// Iterator holds 'version' lock, 'version' is immutable so snapshot
// can be released after iterator created.
return db.newIterator(se.seq, slice, ro)
}