glm-5.3-flash
9bbe6f3ad9
- ADR-009 (new): postgres Large Objects ship as the fs tier's second engine (feature pg-lo, default-off), admitted on POC #7's passed gate (contract 10/10, durable put ~= fs at >=1 MiB, lo_get window gets, transactional LO lifecycle = zero crash orphans). Engine shape: companion table (lo_entries) is the contract authority; put = one tx (lo_create + lowrite + row + pin); get = descriptorless lo_get windows (lo_*64 discipline); named operator deltas (catalog space never returned / autovacuum inherited / sweep for the legacy bypass class only) and named performance deltas (cached-get 20-50x behind page-cache fs single-stream, ~700 MB/s aggregate at 16 readers = the fleet serving picture). - Ripple: backends-and-dispatch (pg-lo shipped; fleet locality contract gains the whole-fleet-pg-lo option), overview (layer map, feature table + pg-lo row, OQ -> shipped pointer), requirements (engine def + REQ-2 note updated), README (current-state + ADR table), store-api (invariant 1/6 engine lists), ADR-008 Status amendment (pg-lo posture superseded by ADR-009), open-questions (audit trail completed: decided -> sequenced -> completed). Verification: docs-only; all cross-references resolve (ADR/REQ/POC); register, findings, spec, and both engine-ADR status lines agree.
178 lines
8.9 KiB
Markdown
178 lines
8.9 KiB
Markdown
---
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status: draft
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last_updated: 2026-10-03
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---
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# Store API
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## What this is
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The store core's public surface: the typed facade above the backends
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that consumers (alkgit, alkfs, the ops module) program against. It owns
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typed keys and hashing (ADR-002), size-threshold dispatch (ADR-003),
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the put-pinning seam, and the liveness/sweep seam (ADR-005) — and
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nothing else: no paths, no manifests, no wire (ADR-004, ADR-001). The
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facade is **engine-blind** (ADR-007/008): which kv/fs engine a node
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runs changes nothing here except fleet-GC mechanism wiring (ADR-008).
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## Public surface
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### Write path
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- **`put(len: Option<u64>, stream)` → `(Key, Pin)`** — the streaming
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put seam (POC #3 finding A1). Two internal paths behind one signature:
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- *Known length* (encouraged, documented as such on the API): the
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preamble hashes before content flows; one pass, no staging needed
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for hashing. Covers git objects, pre-staged files (`stat`-derived
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length), network offers, `Content-Length`-bearing uploads.
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- *Unknown length*: content buffers in memory up to the dispatch
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threshold; on commit the buffer is the whole stored artifact
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(kv tier) — or, on mid-stream threshold overflow, the buffer
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flushes into a stage file and the stream continues into it
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(fs tier — the streaming pass cannot include the preamble, so the
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derivation pass restarts over preamble + staged bytes; forced by
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the preamble being inside the hashed input, not a design choice).
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Verification runs over the eventual stored artifact as a whole;
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a stream error on either path leaves no entry and no stage file.
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Eliminates the A6 dispatch asymmetry by construction: routing is
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a pure function of content length (ADR-003).
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- **Stage-file hygiene invariant** (POC #3 finding A5, codified): every
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failure path converges on stage-discard; every success path converges
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on commit-rename. No early returns that bypass cleanup; this is an
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asserted invariant with dedicated exact-count tests, not review
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hygiene.
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- **`Pin` / `Batch`** — RAII guard on the put path (ADR-005): the
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entry is liveness-protected until the guard drops or the caller
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converts it into a consumer-side reference (registered liveness, a
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root tag). **`Batch`** groups multi-put writes under one batch-scoped
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pin (manifest writes are exactly this); a batch's pins drop together
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on batch commit or drop (ADR-005 §Decision).
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### Read path
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- **`get(key) → Option<(len, stream)>`** — small tier returns a
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bounded read; large tier streams a file handle. Dispatch
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fall-through: a small-tier miss queries the large tier (POC #1
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finding 6).
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- **`stat(key) → Option<EntryMeta>`** — cheap length/type probe
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(phase-0 OQ-BL-04 addendum; gix's header-only read is git's cheapest
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primitive and the packfile-serving surface rides this). `EntryMeta`
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carries `len: u64` and the key's algorithm (the "type" from the
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store's perspective is the hash algorithm — there is no other type at
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this layer). `stat` rides the `Backend` trait's `size` method
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(ADR-008): an indexed-column probe on kv engines, a file stat on the
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fs `local` engine — never a value/content load.
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- **`read_range(key, range) → (slice, slice_digest)`** — slice plus an
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out-of-band slice digest: SHA-256 over the slice bytes, fixed by
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convention so callers and ops handlers agree without negotiation
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(per-range verification against the canonical digest is impossible —
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ADR-006). Range reads fall through tiers exactly as `get` does
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(small-tier miss slices the large tier's value). Local range serving
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(packfiles) is the consumer of this.
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- **`get_stream` / fanout** — the ops module's fetch handler is a
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broadcast above the store: one reader, store arm + subscriber
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arms (POC #3 finding A3); late joiners degrade to normal verified
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`get` after commit. The store exposes the seam; the fanout policy
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lives in the ops layer (ADR-001).
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### Lifecycle
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- **`has(key)`, `delete(key)`** — deletion participates in ADR-005's
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delete windows; direct deletes are permitted but refuse protected
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keys — pinned or re-observed live via registered sources (the same
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per-key arbitration sweeps apply, typed error) — and are unusual by
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posture; most deletion flows through sweeps.
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- **`list() → stream of keys`** — whole-pool enumeration; complete by
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contract (see backends doc for why list correctness is load-bearing).
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- **`register_liveness_source(...)`** — the live-shared GC seam
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(ADR-005, §Decision; the POC's "install implies copy" failure
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(finding 7) is why the verb/name is pinned here).
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- **`sweep() → SweepReport`** — explicit mark-and-sweep; embedders own
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the cadence (ADR-005, no ambient timers). A sweep with no registered
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liveness sources aborts without deleting — the safe default. Under
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a fleet (multiple nodes over one pool — requirements.md REQ-2),
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sweep/put/delete semantics are mechanism-extended by ADR-008: pins
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are DB-backed rows committed atomically with entries, one sweeper
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holds the advisory lock, and delete arbitration is SQL-level — the
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facade's invariant text is unchanged.
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## Error model
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`thiserror`; no panics in library code; no `unwrap`/`expect` outside
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tests (AGENTS convention 2). Distinguished failure families:
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- `Missing` — key absent (get/stat miss)
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- `Verification` — put/get hash-check failure (content ≠ key)
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- `Io(String)` — backend media failure (stringly because
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`std::io::Error` is not stable across versions)
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- `GcAborted` — nothing deleted; sweep not run. Two cause classes
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(ADR-005: a protection source failed; ADR-008: another node holds
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the fleet sweeper lock) — the typed error distinguishes them.
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- `KeyInvalid` — malformed key bytes at the boundary (hashing doc)
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Virgin-store semantics: read paths on a fresh store see absent/empty,
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never "table does not exist" errors (POC #1 finding 2 — the redb
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lesson generalizes to any kv engine).
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## Concurrency posture
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- Async I/O throughout; `tokio::sync` for lifecycle correlation;
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`parking_lot` for short-held internal locks (AGENTS convention 3);
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poisoned locks degrade via `unwrap_or_else(|e| e.into_inner())`.
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- Blocking file work lives in `spawn_blocking` inside backend impls
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(the alkgit trait-execution pattern); the store never blocks the
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executor.
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- The sweep-vs-put window is an architectural mechanism — delete
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windows — specified in ADR-005, not an implementation note.
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## Invariants (the test gate)
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1. Whole-blob put/get round-trips byte-identical under the canonical
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derivation, both tiers, both put paths, **and every shipped engine
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of both tiers** (kv: sqlite + postgres; fs: `local` + pg-lo;
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ADR-007/008/009)
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(interop with real git remains the source of truth, per POC #1's
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lesson about hardcoded vectors).
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2. Dedup: putting identical content twice (same or different path) is
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one pool entry.
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3. Stage hygiene: any failure mid-put leaves zero stage files; any
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success leaves exactly one committed entry.
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4. Sweep safety: with correct liveness registered, sweep counts are
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exact; with aborting sources, sweep deletes nothing. **Engine-gated
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form (ADR-008):** single-node postures assert this under the
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in-process protocol; fleet postures (shared-pool engines) assert it
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under DB-backed pins + the advisory-locked sweep, with the
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exact-count sweep-outcome shape run against dockerized postgres
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under `--all-features`.
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5. `list()` correctness is observable only through GC — list-related
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tests assert through sweep outcomes (POC #1 finding 2's lesson
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codified).
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6. `size`/`stat` on any engine returns the entry length without
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fetching content (asserted per-backend: kv probe, fs stat, pg-lo
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companion-row probe — ADR-008/009).
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## Design Decisions
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| ADR | Decision | Summary |
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|---|---|---|
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| [002](decisions/002-canonical-hash-and-key-encoding.md) | Hashing & keys | derivation + encoding this surface is built on |
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| [003](decisions/003-backend-contract-and-dispatch.md) | Dispatch | routing is a pure function of length; pre-threshold buffering |
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| [005](decisions/005-pooled-cas-and-gc-mechanism.md) | Pools & GC | pins, liveness seams, delete windows, sweep semantics |
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| [006](decisions/006-verification-posture-and-transfer-encoding.md) | Verification | whole-blob checks; slice digests out-of-band |
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| [008](decisions/008-trait-size-probe-fleet-gc-and-fs-engines.md) | Trait `size` + fleet GC | stat/accounting ride the trait's `size` probe; fleet pins/sweeps are engine-backed |
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## Open Questions
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None owned by this document beyond the cross-references above.
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## References
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- `docs/research/poc-largeblob-findings.md` findings A1/A5/A6,
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benchmark table
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- `docs/research/poc-trait-dispatch-findings.md` findings 1–3, 7
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- ADR-003 (put-path buffering), ADR-005 (pin/Batch/Pin lifecycle),
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ADR-006 (range-read semantics), ADR-002 (keys)
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- [ops-surface.md](ops-surface.md) — the fanout/fetch consumer of the
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read path
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- [gc-and-namespaces.md](gc-and-namespaces.md) — the lifecycle seam
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details |