[jira] [Created] (HDDS-3976) KeyValueBlockIterator#nextBlock skips valid blocks

["Ethan Rose (Jira)" <ji...@apache.org>]

Ethan Rose created HDDS-3976:
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             Summary: KeyValueBlockIterator#nextBlock skips valid blocks
                 Key: HDDS-3976
                 URL: https://issues.apache.org/jira/browse/HDDS-3976
             Project: Hadoop Distributed Data Store
          Issue Type: Bug
            Reporter: Ethan Rose
            Assignee: Ethan Rose


HDDS-3854 fixed a bug in KeyValueBlockIterator#hasNext, but introduced another one in KeyValueBlockIterator#nextBlock, which depends on the behavior of that method. When the first key encountered does not pass the filter, the internal nextBlock field is never intialized. Then a call to nextBlock() results in call to hasNext() which returns true, which recursively calls nextBlock() etc until the end of the set is reached and an exception is thrown. This skips all valid keys that may occur past the first invalid key.

This bug was identified while working on HDDS-3869, which adds a strong typing layer before objects are serialized into RocksDB for datanode. Due to RocksDB internals, this changes the database layout so that all prefixed keys are returned at the beginning of the key set, instead of in the end. Since the original layout returned all prefixed keys at the end of the key set, this bug was not evident in any of the original unit tests, since the behavior described above could not occur.

Additionally, the current implementation modifies the internal iterator's state on hasNext() calls, so multiple consecutive hasNext() calls will actually skip over elements. While this is not necessarily a bug, it is atypical iterator behavior and should be resolved to prevent user error.



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