[bug] prefix iterator behavioral inconsistencies

[fansehep]

I test this c++ code:

  std::string key = "your_key";
  std::string value = "dasd";

  int n = 10;
  while (n--) {
    db->Put(rocksdb::WriteOptions(), key, value);
    key += "ad";
  }

  db->Put(rocksdb::WriteOptions(), "1ewadada", "daklda");

  auto prefix_iter = db->NewIterator(rocksdb::ReadOptions());
  prefix_iter->Seek("your_key");

  for (; prefix_iter->Valid(); prefix_iter->Next()) {
    fmt::print("key: {}, value: {}\n", prefix_iter->key().ToString(), prefix_iter->value().ToString());
  }

c++ output:

key: your_key, value: dasd
key: your_keyad, value: dasd
key: your_keyadad, value: dasd
key: your_keyadadad, value: dasd
key: your_keyadadadad, value: dasd
key: your_keyadadadadad, value: dasd
key: your_keyadadadadadad, value: dasd
key: your_keyadadadadadadad, value: dasd
key: your_keyadadadadadadadad, value: dasd
key: your_keyadadadadadadadadad, value: dasd

in rust code:

     db.put("anckjank", "123123dasd").unwrap();
    db.put("1234", "asdasdas").unwrap();
    db.put("12345", "123912031").unwrap();
    db.put("94203u423894", "12312djidjaisd").unwrap();
    db.put("1", "djaklsdalsd").unwrap();
    db.put("000xx-dasd", "123123").unwrap();
    db.put("000xx-dadasdasd", "djaiosdfhjnaiklfjdika").unwrap();

    let prefix_iter = db.prefix_iterator("123");
 
     for it in prefix_iter {
        match it {
            Ok(res) => println!(
                "{} {}",
                String::from_utf8(res.0.to_vec()).unwrap(),
                String::from_utf8(res.1.to_vec()).unwrap()
            ),
            Err(e) => println!("err: {}", e),
        }
    }

rust output:

123 123
1234 asdasdas
12345 123912031
94203u423894 12312djidjaisd
anckjank 123123dasd

we can see the rust output is not equal c++ output. Can someone help me?

[kayabaNerve]

@fansehep Reading the documentation on RocksDBs prefix iteration, the iterator returns Valid()=false when the prefix is no longer present. This Rust library didn't check Valid() properly prior to #829. Updating your lib to a version with that commit may correct the above.

[fansehep]

@fansehep Reading the documentation on RocksDBs prefix iteration, the iterator returns Valid()=false when the prefix is no longer present. This Rust library didn't check Valid() properly prior to #829. Updating your lib to a version with that commit may correct the above.

Really thinks your help. I try the latest rocksdb-rs version. It has been fix it. 😄

[emfax]

I'm finding similar issues with prefix_iterator on the current master branch. I assume that prefix_iterator would iterate over the keys that start with a certain prefix, but it iterates over keys with the prefix as well as every other key that comes after. Am I missing something?

[zaidoon1]

@emfax you are not missing anything, this is the default behaviour, see: https://github.com/facebook/rocksdb/wiki/Prefix-Seek#transition-to-the-new-usage