omnigraph/docs/user/maintenance.md

Maintenance: Optimize, Repair & Cleanup

db/omnigraph/optimize.rs and db/omnigraph/repair.rs.

optimize_all_tables(db) — non-destructive

• Lance compact_files() on every node + edge table on main, then publishes the compacted version to the __manifest so the manifest's table_version tracks the compacted Lance HEAD. Reads pin the manifest version, so without this publish compaction would be invisible to readers and would break the HEAD-vs-manifest precondition of the next schema apply / strict update/delete ("stale view … refresh and retry"). The publish advances the graph version (a system-attributed commit) only for tables that actually compacted.
• Rewrites small fragments into fewer large ones; old fragments remain reachable via older manifests until cleanup runs.
• Each table's compact→publish runs under its per-(table, main) write queue (serializing with concurrent mutations — compaction is a Lance Rewrite op that retryable-conflicts with a concurrent merge/update/delete on overlapping fragments). The Lance-HEAD-before-manifest-publish gap is covered by a SidecarKind::Optimize recovery sidecar (loose-match): a crash in that window rolls the compacted version forward on the next Omnigraph::open (compaction is content-preserving, so roll-forward is always safe).
• Requires a recovered graph. optimize refuses (errors) when an unresolved recovery sidecar is present under __recovery — operating on an unrecovered graph could publish a partial write the open-time recovery sweep would roll back. Reopen the graph to run the recovery sweep, then re-run optimize.
• Uncovered drift is skipped, not interpreted. If a table's Lance HEAD is ahead of the version recorded in __manifest and no recovery sidecar covers that movement, optimize reports skipped: Some(DriftNeedsRepair) with the manifest/head versions and leaves the table untouched. Run omnigraph repair to classify and explicitly publish that drift.
• Bounded by OMNIGRAPH_MAINTENANCE_CONCURRENCY (default 8).
• Returns [TableOptimizeStats { table_key, fragments_removed, fragments_added, committed, skipped, manifest_version, lance_head_version }].
• Blob tables are skipped. A table that declares any Blob property is not compacted: it is reported with skipped: Some(BlobColumnsUnsupportedByLance) (and logged via tracing::warn) instead of compacted, and the rest of the sweep proceeds normally. The current Lance compact_files mis-decodes blob-v2 columns under its forced BlobHandling::AllBinary read; reads and writes are unaffected — only compaction is. This is gated by LANCE_SUPPORTS_BLOB_COMPACTION (db/omnigraph/optimize.rs) and removed when the upstream Lance fix lands (see docs/dev/lance.md). Consequence: fragment count and deleted-row space on blob tables are not reclaimed until then; query results are never affected.

repair_all_tables(db, options) — explicit

• Handles uncovered manifest/head drift: a table's Lance HEAD is ahead of the manifest pin and no recovery sidecar records the writer intent.
• Preview by default. omnigraph repair --json <uri> reports each table's classification, action, manifest/head versions, Lance operation names, and any classification error. --confirm publishes only verified maintenance drift; if any suspicious or unverifiable table is refused, the CLI prints the per-table output and exits non-zero. --force --confirm also publishes suspicious or unverifiable drift after operator review.
• Classifies drift by reading Lance transactions from manifest_version + 1 through lance_head_version. Only ReserveFragments and Rewrite are verified maintenance. Semantic operations such as Append, Delete, Update, Merge, or missing transaction history are not auto-healed.
• Publishes repair by advancing __manifest to the existing Lance HEAD; it does not rewrite Lance data. If the publish succeeds, normal reads and strict writes use the repaired version. If it fails, no new data-side partial state was created.
• Requires a clean recovery state. Pending __recovery sidecars still belong to automatic sidecar recovery, not manual repair.

cleanup_all_tables(db, options) — destructive

• Lance cleanup_old_versions() per table.
• Removes manifests (and their unique fragments) older than the retention policy.
• CleanupPolicyOptions { keep_versions: Option<u32>, older_than: Option<Duration> } — at least one is required.
• Returns [TableCleanupStats { table_key, bytes_removed, old_versions_removed, error }].
• Fault-isolated per table. A single table's transient failure (version GC or orphan reclaim) is recorded on that table's stats row (error: Some(..), logged via tracing) and never aborts the healthy tables — cleanup is the convergence backstop, so it does as much as it can and converges on re-run. The CLI reports any failed tables; rerun cleanup to retry them.
• CLI guards with --confirm; without it, prints a preview line.
• Recovery floor: --keep < 3 may garbage-collect Lance versions that the open-time recovery sweep needs as a rollback target (the sweep restores to the branch's manifest-pinned table version, which is HEAD-1 in the typical Phase B → Phase C drift case). Default --keep 10 is safe.
• Orphaned-branch reconciliation: before the version GC, cleanup runs reconcile_orphaned_branches, which force_delete_branches any per-table or commit-graph Lance branch absent from the manifest branch list. These orphans arise when a branch_delete flips the manifest authority but a downstream best-effort reclaim does not complete (see branches-commits.md). The reconciler is authority-derived and idempotent (it no-ops once nothing is orphaned), runs regardless of the keep_versions / older_than values (those gate version GC only), and never reclaims main or system-branch forks. Reclaimed forks are logged via tracing::info.

Tombstones

Logical sub-table delete markers in __manifest; tombstone_object_id(table_key, version) excludes a sub-table version from snapshot reconstruction.

Internal schema migrations (db/manifest/migrations.rs)

Version evolutions of the on-disk __manifest shape are reconciled automatically on the first write under a new binary. INTERNAL_MANIFEST_SCHEMA_VERSION declares the shape the binary expects; the on-disk stamp omnigraph:internal_schema_version (Lance schema-level metadata) records the on-disk shape. The publisher's open-for-write path calls migrate_internal_schema before reading state; reads are side-effect-free. No operator action is required for in-place upgrades. See storage.md → Internal schema versioning for the full mechanism.

A binary opening a manifest stamped at a version higher than it knows about refuses to publish with a clear "upgrade omnigraph first" error — old binaries cannot clobber a newer schema.