Revision
The per-component MVCC revision-chain subsystem: stores every live version of a
Versioned-mode component in a compact on-disk circular buffer, appends rather than overwrites on every write, and resolves snapshot-isolated reads against that chain by transaction TSN. The same chain backs commit-time conflict detection and is reclaimed — by live garbage collection and by post-crash scrub — once no active transaction can still see an old version.
🔬 Recommended: read in-depth-overview/05-revision.md (Chapter 05: Revision (MVCC)) first to understand the overall design and concepts behind this category, before diving into the specific features below.
Public Features
| Feature | Summary | Status | Level |
|---|---|---|---|
| Revision Append & Chain Growth | Every write to a Versioned component creates a new immutable revision instead of overwriting the old one — Spawn allocates, Write<T>() appends, Destroy tombstones |
✅ Implemented | 🔵 Core |
| MVCC Snapshot Visibility | Reads resolve to the latest revision committed at-or-before the reader's transaction TSN, with read-your-own-writes and explicit RevisionReadStatus outcomes (Success/NotFound/SnapshotInvisible/Deleted) |
✅ Implemented | 🔵 Core |
| Write-Conflict Baseline Tracking | Every chain append records the new and prior revision as the comparison baseline used by commit-time conflict detection and ConcurrencyConflictHandlers |
✅ Implemented | 🟣 Advanced |
| Revision Garbage Collection & Compaction | Bounded-memory chain cleanup keyed off MinTSN, preserving a sentinel for in-flight readers and collapsing fully-dead chains to trigger entity removal |
✅ Implemented | 🟣 Advanced |
Internal Features
| Feature | Summary | Status |
|---|---|---|
| Revision Chain Storage | Per-entity, per-component circular-buffer chunk chain holding every live revision of a Versioned component, allocated on first write and grown on demand |
✅ Implemented |
| Chain Walk Correctness Under Compaction (part of MVCC Snapshot Visibility) | The visibility walk scans the whole chain instead of breaking on the first too-new entry, because background GC compaction can reorder entries without changing their TSNs | ✅ Implemented |
| Crash-Recovery Chain Scrub & Orphan Sweep | Post-crash recovery step that collapses every Versioned chain to its single committed HEAD and frees unreachable revision-table chunks, guaranteeing pre-crash MVCC history never survives into the recovered base |
✅ Implemented |