The COW version-control surface (fork, branches, checkout, commit,
getHistory/streamHistory, asOfCommit, brain.versions) is gone, along with
its subsystems: src/versioning/, the COW object store (CommitLog,
CommitObject, RefManager, TreeObject), HistoricalStorageAdapter, and the
TypeAwareHNSWIndex path it kept alive. The Db API (now/transact/asOf/
with/persist/restore) is the one versioning model in 8.0.
Survivors and replacements:
- BlobStorage survives (the VFS stores file content through it), relocated
to src/storage/blobStorage.ts with binaryDataCodec.ts; its adapter
interface is now BlobStoreAdapter, slimmed to the consumed surface
(write/read/has/delete/getMetadata + MIME-aware compression policy).
- brain.migrate() backup branches are replaced by persist-before-migrate:
MigrateOptions.backupTo persists a hard-link snapshot of the current
generation before any transform runs; MigrationResult.backupPath reports
it, and brain.restore(path) brings it back wholesale.
- CLI: cow.ts (fork/branch/checkout/history/migrate) is replaced by
snapshot.ts — snapshot <path>, restore <path>, history (tx-log),
generation.
- New public read API: brain.transactionLog({limit}) exposes the reified
tx-log (generation/timestamp/meta, newest first) that backs the CLI
history command; TxLogEntry is exported.
Tests: superseded suites deleted; fork/commit blocks excised from shared
suites; BlobStorage tests relocated + reworked against the slimmed store;
migration tests now prove the backupTo snapshot/restore round trip; new
transactionLog coverage in db-mvcc.
One mechanism replaces the COW and versioning subsystems: immutable
generation-stamped records behind a Datomic-style database value.
Record layer (src/db/generationStore.ts):
- Monotonic generation counter in _system/generation.json; bumped once per
transact() commit and once per single-operation write (storage hook), so
brain.generation() is always a meaningful watermark.
- Commit protocol: stage before-images + tx.json delta -> fsync -> execute
batch via TransactionManager -> atomic tmp+rename of _system/manifest.json
(the rename IS the commit point) -> append _system/tx-log.jsonl.
- Crash recovery on open rolls uncommitted generations back byte-identically
and forces an index rebuild; refcounted pins gate compactHistory(), which
records a horizon (asOf below it throws GenerationCompactedError).
Db API:
- Db: get/find/search/related pinned at a generation, with() speculative
overlays, since() diffs, persist() hard-link-farm snapshots, timestamp,
generation, release() + FinalizationRegistry backstop.
- Brainy: now() O(1) pin, transact(ops, {meta, ifAtGeneration}) atomic batch
(GenerationConflictError CAS), asOf(generation|Date|path), restore(path,
{confirm}), compactHistory(), generation(), static open() + load().
- get()/metadata find()/related() are fully correct at any reachable pinned
generation; index-accelerated queries at historical generations throw
NotYetSupportedAtHistoricalGenerationError - never silently-wrong results.
- VersionedIndexProvider (generation/isGenerationVisible/pin/release) in
plugin.ts: feature-detected, balanced pin/release in lockstep with Db
lifecycle, post-commit applier + replay-gap model documented.
Storage primitives (BaseStorage + filesystem/memory adapters): raw-object
read/write/list/remove, fsync barrier, noun/verb raw before-image capture,
tx-log append, snapshotToDirectory (hard-link farm; byte-copy fallback and
append-in-place exceptions), restoreFromDirectory + derived-state reload.
Proof suite (tests/integration/db-mvcc.test.ts + tests/unit/db/): isolation
across 200 mutations, batch atomicity under injected execution failure,
ifAtGeneration CAS, snapshot immunity to source mutation, compaction safety
under pins, with() overlay isolation, generation monotonicity across
reopen, crash consistency through the real recovery path, and versioned
provider pin/release balance. Design record in
docs/ADR-001-generational-mvcc.md.
