// mvccSeek seeks for the first key in db which has a k >= key and a version <=
// snapshot's version, returns kv.ErrNotExist if such key is not found. If exact
// is true, only k == key can be returned.
func (s *dbSnapshot) mvccSeek(key kv.Key, exact bool) (kv.Key, []byte, error) {
// Key layout:
// ...
// Key_verMax -- (1)
// ...
// Key_ver+1 -- (2)
// Key_ver -- (3)
// Key_ver-1 -- (4)
// ...
// Key_0 -- (5)
// NextKey_verMax -- (6)
// ...
// NextKey_ver+1 -- (7)
// NextKey_ver -- (8)
// NextKey_ver-1 -- (9)
// ...
// NextKey_0 -- (10)
// ...
// EOF
for {
mvccKey := MvccEncodeVersionKey(key, s.version)
mvccK, v, err := s.store.Seek([]byte(mvccKey), s.version.Ver) // search for [3...EOF)
if err != nil {
if terror.ErrorEqual(err, engine.ErrNotFound) { // EOF
return nil, nil, errors.Trace(kv.ErrNotExist)
}
return nil, nil, errors.Trace(err)
}
k, ver, err := MvccDecode(mvccK)
if err != nil {
return nil, nil, errors.Trace(err)
}
// quick test for exact mode
if exact {
if key.Cmp(k) != 0 || isTombstone(v) {
return nil, nil, errors.Trace(kv.ErrNotExist)
}
return k, v, nil
}
if ver.Ver > s.version.Ver {
// currently on [6...7]
key = k // search for [8...EOF) next loop
continue
}
// currently on [3...5] or [8...10]
if isTombstone(v) {
key = k.Next() // search for (5...EOF) or (10..EOF) next loop
continue
}
// target found
return k, v, nil
}
}
