Use this skill when implementing or modifying MVCC logic, including version metadata, visibility filtering, and cleanup.
Core principles:
- Reads see a consistent snapshot; writes create new versions.
- Version chains must be ordered and efficiently prunable.
- Visibility is determined by transaction timestamp/epoch and commit status.
Implementation guidance:
- Locate the existing MVCC abstractions (e.g., version metadata types, visibility filters) before adding new logic.
- Ensure reads filter out uncommitted or aborted versions and respect snapshot boundaries.
- When inserting updates, create new version entries rather than in-place mutation.
- For deletes, add tombstones and make them visible using the same MVCC rules.
- Compaction/cleanup must only remove versions that are not visible to any active snapshot.
- Keep metadata lightweight and store large payloads separately if needed.
Common pitfalls:
- Returning uncommitted data to readers.
- Deleting versions still visible to long-running snapshots.
- Mixing wall-clock time with logical timestamps; use the project’s canonical time/epoch source.
When adding new APIs:
- Prefer typed identifiers and enums.
- Keep MVCC filtering in the query path, not at the storage engine boundary unless it is explicitly part of the storage abstraction.