Optimistic concurrency for multi-writer coordination — the read-then-CAS
lock pattern + idempotent-bootstrap singleton inserts. Lands the surface the
SDK scheduler asked for in BRAINY-EXPOSE-TRANSACTIONS, scoped to what ships
cleanly without painting the 8.0 transact() API into a corner.
A. PER-ENTITY _rev FIELD
- src/coreTypes.ts — HNSWNounWithMetadata gains optional `_rev?: number`;
STANDARD_ENTITY_FIELDS includes it so resolveEntityField routes correctly.
- src/types/brainy.types.ts — Entity<T> gains optional `_rev?: number`;
Result<T> mirrors it on the convenience flatten layer.
- src/brainy.ts add() — initializes `_rev: 1` in storageMetadata. New entities
always start at 1.
- src/brainy.ts update() — reads currentRev off the persisted metadata
(falls back to 1 for pre-7.31.0 entities with no _rev), writes
`_rev: currentRev + 1` into the updated metadata. Every successful update()
bumps by exactly 1.
- src/brainy.ts convertNounToEntity + convertMetadataToEntity — both pull
_rev out of the storage metadata and surface it at the top level of Entity.
Pre-7.31.0 entities (no _rev in storage) read as `_rev: 1` so consumers
see a consistent value.
- src/storage/baseStorage.ts — six destructure sites updated to pull _rev
out of the metadata bag so it doesn't leak into customMetadata. Noun-side
returns surface _rev; verb-side destructures correctly but doesn't expose
it on HNSWVerbWithMetadata (verb CAS is future work).
- src/brainy.ts createResult() — flattens entity._rev onto the Result for
backward compat with the existing convenience-field layer.
B. update({ ifRev }) OPTIMISTIC CONCURRENCY
- src/types/brainy.types.ts — UpdateParams<T> gains optional `ifRev?: number`.
- src/transaction/RevisionConflictError.ts (NEW) — carries `{ id, expected,
actual }`. Message names the recipe: refetch with brain.get() and retry
with the latest _rev. Subclass of Error.
- src/brainy.ts update() — when params.ifRev is provided, compares against
currentRev (the rev we just read) and throws RevisionConflictError on
mismatch before any storage write. Omitting ifRev keeps the prior
unconditional-update behavior; existing consumers see no change.
- src/transaction/index.ts — exports RevisionConflictError.
- src/index.ts — public export of RevisionConflictError.
C. add({ ifAbsent }) BY-ID IDEMPOTENT INSERT
- src/types/brainy.types.ts — AddParams<T> gains optional `ifAbsent?: boolean`;
AddManyParams<T> mirrors it as a batch-level flag.
- src/brainy.ts add() — when params.id AND params.ifAbsent, pre-reads
storage.getNounMetadata(id); if present, returns the existing id without
writing. No throw, no overwrite. Ignored when id is omitted (a fresh UUID
can never collide).
- src/brainy.ts addMany() — propagates the batch-level ifAbsent to each
item's add() call. Per-item ifAbsent takes precedence so callers can
override individual rows.
WHAT'S NOT SHIPPED (and why)
A public brain.transaction(fn) wrapper was on the table but was cut. The
internal TransactionManager exposes raw Operation classes (SaveNounMetadata,
etc.) that take StorageAdapter as a constructor argument. A clean high-level
facade in 7.31.0 would have meant either:
(a) Delegate to brain.add() / update() / relate(). Each of those opens its
own internal transaction and commits before the closure returns. Looks
atomic, isn't — a footgun.
(b) Thread an optional `tx?` through every internal write site in
brainy.ts (8 transactionManager.executeTransaction sites). ~2 days of
real refactor with regression surface, and the API shape changes again
in 8.0 anyway.
The SDK scheduler's actual ask (BRAINY-EXPOSE-TRANSACTIONS) is the
read-then-CAS lock pattern. _rev + ifRev solves it completely. Multi-write
atomicity is the 8.0 brain.transact() use case where the Datomic-style
immutable Db makes it atomic by construction — that's the right home.
TESTS
- New tests/integration/rev-and-ifabsent.test.ts (18 tests):
- _rev initialization (1 on add) and surface on get fast/full paths + find
- _rev auto-bump on update across multiple writes
- update({ ifRev }) pass / fail / message format / omitted / legacy-no-rev
- add({ ifAbsent }) writes when absent / no-op when present / id-required
- addMany({ ifAbsent }) propagation + per-item override
- SDK-scheduler scenario: two concurrent CAS updates, one wins one throws
- Unit suite unchanged: 1468/1468.
- All integration subtype + verb + strict + find-limits + new rev suites
pass: 96/96.
DOCS
- New docs/guides/optimistic-concurrency.md (public: true) — full reference:
the lock pattern, read-modify-write retry, idempotent bootstrap, how _rev
interacts with brain.versions, branches/fork, and VFS, what's coming in 8.0.
- docs/api/README.md — add() and update() entries get the new params + tips
pointing at the new guide.
- RELEASES.md v7.31.0 entry.
CORTEX COMPATIBILITY
Zero changes required. _rev is a metadata column already supported by
NativeColumnStore. The auto-bump runs in Brainy JS before any storage call;
Cortex never sees the per-entity counter.
8.0 FORWARD-COMPAT
_rev, ifRev, RevisionConflictError, and ifAbsent survive the 8.0 Db redesign
unchanged. 8.0 layers brain.transact(tx, { ifAtGeneration }) for whole-tx CAS
on top of the same per-entity mechanism — per-entity for single-record
patterns (job locks, idempotent state machines), generation-based for
"did the world move under me." Locked in .strategy/BRAINY-8.0-SUBTYPE-CONTRACT.md § C-6.
Verification
- npx tsc --noEmit: clean
- npm test: 1468 / 1468 unit
- All integration suites including new rev-and-ifabsent: 96/96
- npm run build: clean
- Closed-source product reference audit: clean
David Snelling
bafb4e4caa