omnigraph/docs/dev/index.md
Ragnor Comerford 7d3a52d674
Some checks failed
CI / Classify Changes (push) Has been cancelled
CI / Check AGENTS.md Links (push) Has been cancelled
CI / Container Entrypoint (push) Has been cancelled
Release Edge / Prepare edge release (push) Has been cancelled
CI / Test Workspace (push) Has been cancelled
CI / Test omnigraph-server --features aws (push) Has been cancelled
CI / RustFS S3 Integration (push) Has been cancelled
Release Edge / Build edge omnigraph-linux-x86_64 (push) Has been cancelled
Release Edge / Build edge omnigraph-macos-arm64 (push) Has been cancelled
Release Edge / Build edge omnigraph-windows-x86_64 (push) Has been cancelled
Release Edge / Smoke Windows installer (push) Has been cancelled
feat(engine): WriteTxn - validate schema + open each data table once per write (#298)
* docs(rfc-013): step-3b handoff + §4.1 corrections (validated)

Add the RFC-013 write-path handoff doc, and correct §4.1's WriteTxn sketch from the
4-subagent validation against current code:
- HandleCache → handle-threading (forward the commit-return handle; a version-keyed
  cache misses because HEAD walks N→N+1→N+2 across staging + index-build commits).
- "re-resolution unrepresentable" softened to "pinned base for the pre-commit phase +
  named fresh re-reads at the commit/fork boundary" — three reads (commit-time OCC, the
  live-HEAD drift probe, fork authority) are irreducible correctness machinery.
- WriteParams DOES carry a session field; the real constraint is "stage off an open
  Dataset," so attach the Session by opening read-style then staging off it.

* test(engine): RED step-3b capture-once fitness asserts + open_count probe

Two write-path cost gates, RED today, GREEN after the WriteTxn lands:
- write_validates_schema_contract_once: a write must validate the schema contract
  once (3 read_text + 2 exists). Today re-validates at every resolve point —
  measured 12 read_text / 9 exists (~4 validations) via CountingStorageAdapter
  (zero production change; the write twin of the read-path schema-once test).
- keyed_insert_opens_table_at_most_once: a keyed single-table write must open its
  table <=1x. Today measured 10 opens.

Adds an exact open-CALL probe: open_count + record_open() on QueryIoProbes (mirroring
probe_count/record_probe), called at both open chokepoints; surfaced as
IoCounts.open_count. forbidden_apis guarantees every write open routes through them.

* feat(engine): WriteTxn carrier + open_write_txn (3b scaffolding)

The capture-once write transaction (RFC-013 step 3b): WriteTxn{branch, base:
Snapshot, session} + Omnigraph::open_write_txn, which validates the schema contract
once and pins the base snapshot + the shared per-graph Session.

Landed as reviewed scaffolding (gated #[allow(dead_code)]); the next pass threads
Option<&WriteTxn> through open_for_mutation_on_branch / staging on the non-strict
bound-branch path — opening the base once from the pinned entry with the warm session
(a session-aware pinned opener returning a SnapshotHandle) and skipping the per-table
schema re-validation — to turn the two RED cost gates green. Strict ops / fork / the
commit-time OCC re-read keep their fresh reads.

* test(engine): scope write-path open_count to data tables (RFC-013 step 3b)

The keyed_insert_opens_table_at_most_once gate asserted open_count <= 1, but
open_count was a single unclassified counter: record_open() fires in both
open chokepoints, and open_dataset_tracked also opens the internal/system
tables (__manifest via layout.rs, _graph_commits/_graph_commit_actors via
commit_graph.rs). So the count conflated data-table opens with the publisher
CAS + commit-graph append opens — making the gate measure the wrong quantity
and unreachable by threading alone (the manifest publish keeps it >1 regardless).

Scope it by table class, mirroring the read-side counters (which already split
by URI prefix via separate wrappers): record_open(uri) classifies the open's
last path segment and feeds data_open_count vs internal_open_count. IoCounts
exposes both; the gate now asserts data_open_count <= 1.

Re-baselined: a single keyed insert is data_open_count=4 / internal_open_count=6
(sum 10, the old conflated value). The RED target for the WriteTxn threading is
now the real data-table-open count (4 -> 1), with internal opens correctly out
of scope. Pure test-harness/instrumentation; no production behavior change
(classification runs only inside the probe closure, skipped when no probes are
installed).

Also marks #297 (optimize-vs-write race) as landed in the step-3b handoff —
this branch is already stacked on origin/main after it merged.

* feat(engine): validate the schema contract once per write (RFC-013 step 3b)

A single mutate/load re-validated the schema contract ~4 times: at the entry
(ensure_schema_state_valid), per-table in open_for_mutation_on_branch
(resolved_branch_target), at the commit-time OCC re-read (fresh_snapshot_for_branch),
and in the publisher's index-build snapshot (snapshot_for_branch). Each validation
is 3 read_text + 2 exists on the storage adapter — O(touched resolve-points) of
redundant contract I/O on every write.

Thread the already-landed WriteTxn carrier through the write path: capture
`txn = open_write_txn(branch)` once at the mutate/load entry (the single validation),
then source the per-table entry and the commit/publish snapshots from `txn.base`
instead of re-resolving. When `txn` is None (branch merge, schema apply, tests) every
function is byte-identical to before.

- mutate_with_current_actor / load_jsonl_reader capture txn once (replacing the
  entry-point ensure_schema_state_valid) and thread Some(&txn) through
  execute_*/open_table_for_mutation, commit_all, and
  commit_updates_on_branch_with_expected.
- open_for_mutation_on_branch sources (snapshot, branch) from txn.base/txn.branch
  when present — skipping resolved_branch_target's re-validation. The OPEN itself is
  unchanged (still HEAD via open_dataset_head_for_write), and strict ops keep
  ensure_expected_version. Schema-once applies to strict and non-strict alike; the
  data-open collapse is a separate change.
- commit_all uses fresh_snapshot_for_branch_unchecked (the OCC manifest re-read minus
  the schema re-validation) when txn is present; the drift guard is unchanged.
- prepare_updates_for_commit uses txn.base for the publisher index-build snapshot.

fresh_snapshot_for_branch{,_unchecked} now read the manifest directly via
ManifestCoordinator instead of resolve_target. The OCC re-read consumes only the
Snapshot (per-table location + version), which ManifestCoordinator::open().snapshot()
produces identically — but resolve_target additionally opened the commit graph (a
spurious _graph_commits.lance exists probe the OCC read never consults). Dropping that
load is a pure read-cost reduction for every fresh-snapshot caller (commit_all's None
arm, optimize, repair, fork reclaim); the returned Snapshot is unchanged and the read
is a fresher cold manifest re-read, so the OCC freshness guarantee is preserved.

Greens write_validates_schema_contract_once (3 read_text / 2 exists, was 12/9).
keyed_insert_opens_table_at_most_once stays red (data_open_count=4) — the open
collapse lands next. Full engine suite green otherwise.

* feat(engine): open each data table once per write (RFC-013 step 3b)

A single keyed-node mutate opened its data table 4 times: accumulation (to read
.version()), staging (the real write base), the commit-time drift guard (to read
live HEAD), and the publisher's index build (reopen at the just-committed version).
Collapse three of the four — using the WriteTxn carrier threaded for schema-once —
so a write opens each touched data table at most once.

- #1 accumulation: open_for_mutation_on_branch now returns
  (Option<SnapshotHandle>, expected_version, full_path, table_branch). On the txn's
  own branch, a non-strict (Insert/Merge) op needs no open — the only thing the
  caller reads is .version() (the CAS fence), which is exactly the pinned base
  version (entry.table_version). So skip open_dataset_head_for_write and source the
  version from txn.base. The node insert path already discarded that handle; the
  edge path resolves a pinned read only when non-default cardinality needs it.
  STRICT ops and any write that must fork still open live HEAD + ensure_expected_version.
- #3 commit drift guard: commit_all reads live HEAD via
  entry.dataset.dataset().latest_version_id() — a cheap manifest-pointer probe off
  the already-open staging handle (the same primitive ManifestCoordinator::
  probe_latest_version uses) instead of a fresh open_dataset_head_for_write. The
  head<current / head>current drift classification is byte-identical.
- #4 index build: commit_all now returns the per-table post-commit_staged
  SnapshotHandle map; commit_updates_on_branch_with_expected threads it into
  prepare_updates_for_commit, which builds indices on the threaded handle instead of
  reopening at the same just-committed version. Absent a handle (other writers,
  inline/delete tables) the reopen path is byte-identical.

When txn is None (branch merge, schema apply, tests) every function opens and checks
exactly as before. Greens keyed_insert_opens_table_at_most_once (data_open_count 4->1).
Schema-once gate stays 3/2. Full engine suite + failpoints (recovery sidecar lifecycle)
green.

* refactor(engine): name the write-path open/commit returns (RFC-013 step 3b)

The open collapse left two positional returns that are easy to mis-thread and
carry an unwritten contract: open_for_mutation_on_branch's
(Option<SnapshotHandle>, u64, String, Option<String>) and commit_all's 5-tuple
(updates, expected_versions, sidecar_handle, guards, committed_handles). Replace
both with named structs so each field reads at the call site and the Option's
contract is documented, not folklore.

- OpenedForMutation { handle, expected_version, full_path, table_branch } with a
  require_handle(ctx) helper for the callers that must have a handle (strict ops,
  the fork path, every no-txn caller — branch merge, the seed test). The handle is
  None only on the non-strict-txn open-skip path (collapse #1); require_handle
  panics with a named context if that contract is ever broken.
- CommittedMutation { updates, expected_versions, sidecar_handle, guards,
  committed_handles } for commit_all; consumers destructure into the same local
  bindings they already used, so the publish/sidecar/guard-hold logic is unchanged.
- A debug_assert in open_table_for_mutation pins the skip contract: a missing handle
  is legal only on the non-strict txn path, so a future strict arm returning None
  trips in debug builds instead of handing None to a require_handle consumer.

Pure refactor — no behavior change. Both cost gates stay green (schema 3/2,
data_open_count=1), full engine suite + lib (162) green.

* refactor(engine): drop the unearned session field from WriteTxn (RFC-013 step 3b)

The open collapse greens data_open_count<=1 by SKIPPING the accumulation open,
PROBING live HEAD with latest_version_id, and REUSING the commit_staged handle —
none of which consume a session. The captured WriteTxn.session was therefore dead
(`#[allow(dead_code)]`): unearned surface a reviewer rightly flags.

Remove it. The carrier is now {branch, base} — exactly what schema-once + the open
collapse use. Step 5 (PublishPlan unification) makes WriteTxn the non-optional
publish carrier and is the right home for session-aware base opens, where the
warm-session benefit on the single remaining open — an object-store (S3) phenomenon,
invisible on local FS — can be earned by its own cost gate rather than carried dead
through this PR.

No behavior change; both cost gates stay green (schema 3/2, data_open_count=1).

* docs(rfc-013): mark step 3b DONE — schema-once + open-collapse shipped, session deferred to step 5

* docs(rfc-013): capture the write-base-staleness convergence (§1d)

Three findings this cycle share one root — the write base is a stale, un-probed,
un-classified pin (the read path probes; the write path returns the warm
coordinator snapshot):

- #298 edge-@card stale-read regression (cursor High / codex P1, VALID): collapse #1
  made the cardinality scan read txn.base instead of live HEAD, so a concurrent edge
  is uncounted and a max can be exceeded. Fix on #298: restore the live-HEAD read +
  deterministic test + correct the single-writer doc comment.
- The structural liability underneath: no unified write-validation read-set —
  endpoint/cardinality/uniqueness each pick freshness ad hoc (warm/pinned/live),
  the same cardinality check forks mutation-vs-loader, none re-validated at commit.
- The served-strict-write stale-view false-fail (validated on prod + a #[ignore]
  repro): a strict update/delete false-fails ExpectedVersionMismatch after an external
  optimize advance — the write-side mirror of #297/§6.6. The naive blanket probe is
  proven wrong (breaks the cross-process lost-update OCC contract).

All three converge on Design A (step 5): open_txn's warm probe makes the base fresh,
the op-class-aware precondition (derive maintenance vs logical from Lance per-version
transaction metadata — no parallel marker) fast-forwards maintenance and fails logical,
and §7.1's read-set-in-CAS unifies + re-validates the validation read-set. §8 records
the #298 follow-up, the widened §7.1 scope, and the step-5 two-test acceptance contract.

* test(engine): RED — edge @card must scan live HEAD, not stale txn.base (#298)

Regression guard for the cursor-High/codex-P1 finding on #298: 3b's collapse #1
made the non-strict edge-insert cardinality scan read the pinned txn.base instead
of live HEAD (edge_cardinality_read_handle), so a concurrent edge committed after
txn capture is uncounted and a @card max is silently exceeded (invariant 9).

Deterministic two-handle test (no failpoint): handle A commits WorksAt(Alice->Acme)
to the @card(0..1) max; stale handle B (never read since) inserts a second WorksAt
for Alice. B's coordinator is stale by construction (the write path doesn't probe),
so B scans txn.base (Alice has 0) and wrongly commits the 2nd edge. RED: the insert
that must be rejected currently succeeds (panics at unwrap_err). Goes green when the
scan reads live HEAD.

* fix(engine): scan live HEAD for edge @card, not the pinned txn.base (#298)

3b's collapse #1 skips the non-strict edge accumulation open, so edge_cardinality_
read_handle reopened the edge table at the pinned txn.base for the @card scan. Since
cardinality is validated once (never rechecked at commit), a concurrent edge committed
after txn capture was uncounted and a @card max could be silently exceeded (invariant
9) — the cursor-High/codex-P1 regression on #298. Pre-3b the scan read live HEAD (the
mutation's own open_dataset_head_for_write handle).

Restore the live-HEAD read: take the table LOCATION from the pinned entry (stable
across versions) and open the dataset at its current HEAD via open_dataset_head_for_
write. Gate-safe — the data_open_count / merge-insert-only gates are node inserts; the
edge cardinality path (non-default @card only) is untouched by them, and the extra
live-HEAD open is exactly the pre-3b shape. Also drops the dead None-fallback's schema
re-validation (greptile P2, auto-resolved). The residual validate->commit TOCTOU is the
pre-existing §7.1 gap (RFC-013 step 4), recorded in handoff §1d/§8.

Turns cardinality_rejected_for_stale_handle_after_concurrent_edge_commit green;
validators / write_cost / writes / consistency / end_to_end / branching all green.

* docs(dev): link handoff docs from index

* docs(engine): tighten 3b claims to match the code (#298 review)

Review caught several comments/docs overclaiming what the code does (the session
drop + the #298 cardinality fix left stale/too-strong wording). No logic change.

- open_write_txn doc: drop the stale "shared per-graph Session" (WriteTxn no longer
  carries one); scope "once" to the table-touch hot path and note edge/load RI
  validation still re-resolves (→ step 4 §7.1) + the session-aware open is step 5.
- edge cardinality call-site comment: it said the scan uses a "pinned txn.base" — it
  now opens LIVE HEAD (#298); corrected.
- write_cost.rs: "opens the base once (with the shared Session)" → session-aware base
  open is deferred to step 5.
- data_open_count completeness (instrumentation.rs + write_cost.rs): forbidden_apis
  only keeps engine code OUTSIDE the storage layer on the chokepoints; table_store.rs
  is allow-listed and holds direct Dataset::opens for branch-management ops (not the
  keyed-write hot path the gate measures). Narrowed the claim accordingly.
- handoff §4: "schema once / open once" is the node hot path (the two gates); edge
  endpoint + loader RI/cardinality still re-validate and read warm — #298 un-regresses
  cardinality only, it does NOT close write-validation freshness (that's step 4 §1d/§7.1).

build clean; write_cost / validators / forbidden_apis green.
2026-06-23 21:27:31 +02:00

7 KiB

Developer Docs

Audience: contributors, maintainers, and coding agents

This is the contributor-facing entry point. These docs explain architecture, invariants, implementation contracts, test ownership, and upstream Lance constraints. User-facing behavior should still be documented through docs/user/index.md and the relevant public reference docs.

Required For Every Non-Trivial Change

Need Read
Architectural rules, known gaps, deny-list invariants.md
Upstream Lance source-of-truth index lance.md
Existing test coverage and test placement testing.md

Architecture And Storage

Area Read
System structure, L1/L2 framing, component diagrams architecture.md
On-disk layout, manifest schema, URI behavior storage.md
Direct-publish writes, D2, staged writes, recovery sidecars writes.md
Query execution, mutation execution, loader flow execution.md
Index lifecycle and graph topology indexes indexes.md
Branch and commit internals branches-commits.md
Three-way merge implementation and conflicts merge.md
Diff/change-feed implementation changes.md
Branch protection policy branch-protection.md

Language, Runtime, And Boundaries

Area Read
Schema grammar, catalog, migration planner schema-language.md
Query grammar, IR, lints, mutation restrictions query-language.md
Embedding client and @embed integration embeddings.md
Cedar policy surface and server gating policy.md
Server auth, OpenAPI, endpoint handlers server.md
Error taxonomy and serialization errors.md
Constants and tunables constants.md
Transaction model public contract transactions.md
User-doc coherence cleanup ledger docs-issues.md

Project Operations

Area Read
CI and release workflows ci.md
Install and deployment packaging install.md, deployment.md
Release history releases/

Contribution & Governance

Area Read
How to contribute (external) CONTRIBUTING.md
Governance model, roles, decision authority GOVERNANCE.md
Public contribution RFC track rfcs/

The docs/rfcs/ track is the public, externally-authorable RFC process. The maintainer/internal RFCs below (rfc-00N-*.md) are a separate, team-owned track; don't conflate the two.

Case Studies

Worked write-ups of specific bugs — root cause, fix, and the reasoning that ruled out the tempting-but-wrong alternatives. Read these for the debugging pattern, not just the outcome.

Area Read
camelCase property filters lowercased at runtime (#283) — two engine→Lance boundaries, two different fixes bug-case-fix.md

Active Implementation Plans

Working documents for in-flight feature work. Removed when the work lands.

Area Read
Schema-lint chassis v1 (MR-694) — --allow-data-loss, soft/hard drops schema-lint-v1-plan.md
Inline + stored queries, request/response envelope, MCP (MR-656 / MR-976 / MR-969) rfc-001-queries-envelope-mcp.md
Config & CLI architecture — layered config, client targeting, file naming (MR-973 / MR-974 / MR-981) rfc-002-config-cli-architecture.md
MCP server surface — full tool parity, stored queries, modular auth (MR-969 / MR-956 / MR-974) rfc-003-mcp-server-surface.md
Future cluster control plane — declarative as-code config, JSON state ledger, reconciler cluster-config-specs.md, cluster-axioms.md, cluster-config-implementation-spec.md
Cluster graph & schema apply — Phase 4 sidecars, roll-forward recovery, approval artifacts rfc-004-cluster-graph-schema-apply.md
Server boots from cluster state — Phase 5 mode switch, applied-revision serving rfc-005-server-cluster-boot.md
Per-operator config — ~/.omnigraph/ identity, keyed credentials, named servers (the operator slice of RFC-002) rfc-007-operator-config.md
Deprecate omnigraph.yaml — one concern per config surface; key-by-key migration map and staged retirement rfc-008-deprecate-omnigraph-yaml.md
Unify CLI embedded/remote access paths — parity referee, shared wire-DTO crate, GraphClient trait, declared plane capabilities rfc-009-unify-access-paths.md
Restructure the CLI around explicit planes — one graph-addressing model, declared capability surface, plane-grouped help (expands RFC-009 Phase 4) rfc-010-cli-planes-restructure.md
CLI refactoring — one addressing & config model post-omnigraph.yaml: scope + --graph + derived access path, served-default / privileged-direct, profiles, named queries, capability classifier (completes RFC-008) rfc-011-cli-refactoring.md
Provider-independent embedding configuration — one resolved EmbeddingConfig + sealed provider enum (Gemini/OpenAI/Mock), identity recorded in the schema IR, query-time same-space validation, NFR floor rfc-012-embedding-provider-config.md
Write-path latency — capture-once WriteTxn, version-pinned opens, one GraphPublishAuthority fed declarative PublishPlans, manifest-authoritative lineage, epoch fence, bounded history (compaction + cleanup), and an IO-counted cost contract (iss-write-s3-roundtrip-amplification, iss-991) rfc-013-write-path-latency.md
RFC-013 handoff — current-state map, latest validation, and concrete next actions for finishing write-path latency and correctness work handoff-rfc-013-write-path.md
Schema-apply recovery flake handoff — investigation notes and validation plan for the intermittent schema-apply reopen race handoff-schema-apply-recovery-flake.md

Boundary

Developer docs may mention implementation details, stale gaps, upstream Lance blockers, and review rules. User docs should not require that context unless the detail changes the public contract.