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.