Iterator

Error Handling

Iterator::status() returns the error of the iterating. The errors include I/O errors, checksum mismatch, unsupported operations, internal errors, or other errors.

If there is no error, the status is Status::OK(). If the status is not OK, the iterator will be invalidated too. In another word, if Iterator::Valid() is true, status() is guaranteed to be OK() so it's safe to proceed other operations without checking status().

On the other hand, if Iterator::Valid() is false, there are two possibilities: (1) We reached the end of the data. In this case, status() is OK(); (2) there is an error. In this case status() is not OK(). It is always a good practice to check status() if the iterator is invalidated.

Prefix Iterating

Prefix iterator allows users to use bloom filter or hash index in iterator, in order to improve the performance. However, the feature has limitation and may return wrong results without reporting an error if misused. So we recommend you to use this feature carefully. For how to use the feature, see Prefix Seek

Iterating upper bound

You can specify an upper bound of your range query by setting ReadOptions.iterate_upper_bound for the read option passed to NewIterator(). By setting this option, RocksDB doesn't have to find the next key after the upper bound. In some cases, some I/Os or computation can be avoided. In some specific workloads, the improvement can be significant. Note it applies to both of forward and backward iterating.

See the comment of the option for more information.

Coming soon...