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932334ba01
Update the doc surface to reflect MR-847 having shipped end to end —
sidecar protocol, classifier, all-or-nothing decision tree, roll-forward
via ManifestBatchPublisher, roll-back via Dataset::restore with
fragment-set short-circuit, audit trail in
_graph_commit_recoveries.lance, OpenMode::{ReadWrite, ReadOnly}, and
the four migrated writers all carrying sidecars across Phase B → Phase C.
- docs/invariants.md §VI.23: change from "upheld at the writer-trait
surface for inserts/updates/etc., per-table commit_staged → manifest
publish window remains" to "upheld at the writer-trait surface AND
across process boundaries". The MR-847 sweep closes the residual on
the next Omnigraph::open. The "continuous in-process" property
(no ExpectedVersionMismatch surfacing to subsequent writers between
Phase B failure and process restart) is honest follow-up at MR-856.
- docs/runs.md: replace "Finalize → publisher residual" section with
"Open-time recovery sweep (MR-847)" — describes the sidecar protocol
lifecycle (Phases A-D), the sweep's classifier + decision dispatch,
the audit trail, and the operator-facing query
(omnigraph commit list --filter actor=omnigraph:recovery).
- AGENTS.md capability matrix "Atomic single-dataset commits" row:
drop the "Layer (3) is not yet shipped — tracked in MR-847" caveat;
describe the three layers as all shipping; reference MR-856 for the
background-reconciler follow-up.
- docs/storage.md: add _graph_commit_recoveries.lance and
__recovery/{ulid}.json to the on-disk layout (mermaid + prose).
- docs/branches-commits.md: new "Recovery audit trail (MR-847)"
subsection describing the join from
_graph_commits.lance:actor_id="omnigraph:recovery" to
_graph_commit_recoveries.lance:graph_commit_id for operator
post-mortem.
- docs/maintenance.md: note the MR-847 recovery floor on cleanup —
--keep < 3 may garbage-collect Lance versions the recovery sweep
needs as a rollback target. Default --keep 10 is safe.
- docs/testing.md: add tests/recovery.rs to the engine integration-test
table; expand the failpoints.rs row to mention the four MR-847
per-writer Phase B → recovery integration tests.
- .context/mr-847-design.md: prepend a "Status: DONE" stanza listing
every commit hash + scope across phases 1-10.
AGENTS.md ↔ docs/ cross-link check passes (26 links, 26 docs).
Full workspace test sweep passes with --features failpoints (361 tests
across 20 binaries).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
63 lines
4 KiB
Markdown
63 lines
4 KiB
Markdown
# Branches, Commits, Snapshots
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## L1 — Lance per-dataset branches
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Lance supports branching at the dataset level: a branch is a named lineage of versions, and `fork_branch_from_state(source_branch, target_branch, source_version)` creates a copy-on-write fork.
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## L2 — Graph-level branches
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OmniGraph builds *graph branches* on top by branching every sub-table coherently:
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- `branch_create(name)` / `branch_create_from(target, name)` — disallowed name `main`; fails if branch exists; ensures the schema-apply lock is idle.
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- `branch_list()` — returns public branches, **filters internal** `__run__…` and `__schema_apply_lock__` prefixes.
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- `branch_delete(name)` — refuses if there are descendants or active runs on the branch; cleans up owned per-branch fragments.
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- **Lazy forking**: a branch only forks a sub-table when that sub-table is first mutated on it. Pure-read branches share fragments with their source.
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- `sync_branch(branch)` — re-binds the in-memory handle to the latest head of the branch.
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## L2 — Commit graph (`db/commit_graph.rs`)
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In-memory shape of a graph commit:
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```
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GraphCommit {
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graph_commit_id: ULID,
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manifest_branch: Option<String>,
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manifest_version: u64,
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parent_commit_id: Option<String>,
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merged_parent_commit_id: Option<String>, // populated for merge commits
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actor_id: Option<String>, // joined in-memory from _graph_commit_actors.lance, NOT a column on _graph_commits.lance
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created_at: i64 (microseconds since epoch),
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}
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```
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Storage is split across two Lance datasets (both with stable row IDs):
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- `_graph_commits.lance` — every column above *except* `actor_id`.
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- `_graph_commit_actors.lance` — optional separate `(graph_commit_id, actor_id)` map, created on demand. The `actor_id` field above is populated by joining this dataset in-memory at load time.
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Notes:
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- Every successful publish (load / change / merge / schema_apply) appends one commit.
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- Merge commits have two parents; linear commits have one.
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- API: `list_commits(branch)`, `get_commit(id)`, `head_commit_id_for_branch(branch)`.
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## L2 — Snapshots & time travel
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- `snapshot()` — current snapshot for the bound branch; cached.
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- `snapshot_of(target)` — snapshot at a `ReadTarget` (branch | snapshot id).
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- `snapshot_at_version(v: u64)` — historical snapshot from any manifest version.
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- `entity_at(table_key, id, version)` — single-entity time travel without building a full snapshot.
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- A `Snapshot` is a `(version, HashMap<table_key, SubTableEntry>)` — cheap to build, snapshot-isolated cross-table reads.
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## L2 — Internal system branches
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Filtered from `branch_list()` but visible to internals:
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- `__schema_apply_lock__` — serializes schema migrations.
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- `__run__<run-id>` — legacy from the pre-v0.4.0 Run state machine (removed in MR-771). The branch-name guard predicate `is_internal_run_branch` is kept as defense-in-depth so users cannot create a branch matching the legacy prefix; the filter will be removed once production legacy branches are swept (MR-770).
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## L2 — Recovery audit trail (MR-847)
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The four migrated writers (`MutationStaging::finalize`, `schema_apply`, `branch_merge`, `ensure_indices`) protect their multi-table commits with a sidecar at `__recovery/{ulid}.json` written before Phase B and deleted after Phase C. The next `Omnigraph::open` (gated on `OpenMode::ReadWrite`) runs the recovery sweep in `crates/omnigraph/src/db/manifest/recovery.rs`: classify per-table state, decide all-or-nothing per sidecar, roll forward / back, record an audit row.
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Audit rows live in `_graph_commit_recoveries.lance` (sibling to `_graph_commits.lance`) and reference the commit graph by `graph_commit_id`. The linked `_graph_commits.lance` row carries `actor_id="omnigraph:recovery"` (the system actor). To find recoveries for a specific original actor: `omnigraph commit list --filter actor=omnigraph:recovery`, then join to `_graph_commit_recoveries.lance` by `graph_commit_id` to read `recovery_for_actor`. Schema: see `crates/omnigraph/src/db/recovery_audit.rs`.
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