OpenFile(path) opens or creates a WAL, replays its valid records into memory, then positions the file for appending. Each successful mutation is recorded and synced before the in-memory map is changed.

Record framing#

Each record has a 12-byte header followed by a payload:

The payload begins with an operation byte. For set, del, rename, and copy, the remaining bytes encode an entry: two little-endian uint32 lengths, then key bytes and value bytes. clear has only its operation byte. Entries are limited to 64 MiB.

Replay and errors#

Replay applies records in order. A final incomplete header or payload is treated as a truncated tail and removed before appending resumes. Invalid magic, an invalid size, a checksum mismatch, or an invalid complete operation returns an error instead of silently replaying past the corruption.