Status: IN
The in-memory `keydir` dict is the only index; every live key has exactly one `KeyEntry` pointing to its most recent non-tombstone record on disk.
Source: entries/2026/05/28/hash-index-storage-bitcask.md
self._index: dict[str, tuple[str, int]] = {} # key -> (filepath, offset)
# all reads go through: filepath, offset = self._index[key]