feat: flat-subtree drop — O(1) removal of a populated subtree with staged range-tombstone reclamation (#848) - #849
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…aged range-tombstone reclamation (#848) Adds the flat-drop primitive requested by issue #848, specialized to the case platform actually has: the dropped subtree is declared to contain no child subtrees (a contract that holds by construction for non-Merk data trees and indexed primaries), so no discovery walk, sweep queue, or budgeted background pass is needed. Consensus side (GROVE_V4, fail-closed capability gates): - GroveDb::drop_flat_subtree(path, key): an ordinary layered delete of the subtree's element from its parent Merk — the child is never opened, so the cost is O(1) in the subtree's contents — plus one durable redo record staged into a reserved namespace of the (previously unused) meta column family, committed atomically with the delete via the same StorageBatch. The record carries the subtree's full path and every doomed prefix: the path-derived primary and, for indexed primaries, the three axis secondaries (blake3(prefix ‖ axis_tag)). - SubelementsDeletionBehavior::DropFlat on batch DeleteTree ops: same semantics through apply_batch / apply_partial_batch, classified from the captured ACTUAL stored type (V4 old-value observer), with average/worst-case estimates extended by the record's deterministic put cost (estimation is replay-critical). Reclamation (outside consensus, never in returned costs): - RocksDbStorage::delete_prefix_ranges: one DB-level range tombstone per (prefix, CF) across all four column families. Optimistic transactions cannot carry DeleteRange, so tombstones are written post-commit: immediately when GroveDB owns the transaction, else at the host's next GroveDb::flush_pending_prefix_drops (also the crash-recovery entry point — records survive restarts and checkpoints, and draining is idempotent: tombstones are re-issued before the record is removed). - Drain-time liveness guard: a record whose path resolves to a live element (a re-created dropped path — a documented contract violation) is skipped and reported, degrading the violation to a bounded leak instead of destroying live data. Orphan invisibility holds by construction: state sync walks the element graph from the root and never ships unreachable prefixes, verify_grovedb recurses from the root, every iterator is prefix-scoped, and the meta CF is outside the root hash — so nodes at different reclamation progress share identical root hashes. Tests: storage-level codec/namespace/range-delete units; version-gate pins (0 on V1..V3, 1 on V4); and 14 grovedb integration tests covering content-independent cost, indexed-secondary reclamation, tx atomicity and rollback, deferred drain, crash resume, recreate-path poisoning, and batch atomicity. Full workspace suite: 5180 passed, 0 failed. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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📝 WalkthroughWalkthroughAdds version-gated flat subtree deletion for standalone and batch operations. The change detaches tree elements in O(1), records storage prefixes durably, reclaims storage with range tombstones, integrates transaction handling, and adds storage and behavior tests. ChangesFlat subtree deletion
Estimated code review effort: 4 (Complex) | ~60 minutes Merge Risk: 🟡 Moderate · up to The flat-subtree deletion behavior may regress proof or reference-integrity contracts without dedicated coverage, and feature-disabled builds may not compile due to invalid re-exports. The PR is not merge-ready until these bounded issues are addressed or explicitly accepted. Sequence Diagram(s)sequenceDiagram
participant Caller
participant GroveDb
participant ParentMerk
participant RocksDbStorage
Caller->>GroveDb: drop_flat_subtree(path, key)
GroveDb->>ParentMerk: remove subtree element
GroveDb->>RocksDbStorage: write pending prefix-drop record
GroveDb->>RocksDbStorage: commit atomic batch
GroveDb->>RocksDbStorage: flush_pending_prefix_drops()
RocksDbStorage-->>GroveDb: reclamation report
GroveDb-->>Caller: operation result
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Linked Issues checkExplanation The PR implements the flat-subtree portion of issue Resolution Implement the missing nested-subtree discovery and budgeted, resumable sweep requirements from issue Full details: Out of Scope Changes checkExplanation The changes are generally related to the flat-subtree drop feature. The storage queue, version gates, cost estimates, documentation, re-exports, transaction helper, and tests support the requested implementation and do not show unrelated functionality. ✨ Finishing Touches📝 Generate docstrings
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Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
## develop #849 +/- ##
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Coverage 92.57% 92.58%
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Files 296 297 +1
Lines 91688 92199 +511
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+ Hits 84876 85358 +482
- Misses 6812 6841 +29
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In `@grovedb/src/operations/delete/mod.rs`:
- Around line 37-38: Move each minimal feature gate before its associated
re-export: in grovedb/src/operations/delete/mod.rs lines 37-38, gate the
PendingPrefixDropsReport re-export from flat_drop; in grovedb/src/lib.rs lines
255-256, gate the operations::delete::PendingPrefixDropsReport re-export. Ensure
both re-exports are excluded when the minimal feature is disabled.
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grovedb-version/src/tests.rsgrovedb-version/src/version/grovedb_versions.rsgrovedb-version/src/version/v1.rsgrovedb-version/src/version/v2.rsgrovedb-version/src/version/v3.rsgrovedb-version/src/version/v4.rsgrovedb/src/batch/estimated_costs/average_case_costs.rsgrovedb/src/batch/estimated_costs/worst_case_costs.rsgrovedb/src/batch/mod.rsgrovedb/src/lib.rsgrovedb/src/operations/delete/flat_drop.rsgrovedb/src/operations/delete/mod.rsgrovedb/src/tests/flat_drop_tests.rsgrovedb/src/tests/mod.rsgrovedb/src/util.rsstorage/src/rocksdb_storage.rsstorage/src/rocksdb_storage/storage.rs
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…comment attached to its re-export - estimates_dominate_actual_for_drop_flat: both batch estimators must dominate the actual cost of a DropFlat batch in every dimension (exercises add_flat_drop_record_put_estimate and both estimator injection sites). - apply_operations_without_batching_routes_drop_flat: covers the DropFlat arm of the non-batching apply path. - lib.rs: cargo fmt had slotted the new PendingPrefixDropsReport re-export between an existing doc comment and the item it documents; give the new re-export its own doc comment above the old one. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Makes explicit what was previously implicit (and verified against the actual producers): DontCheckWithNoCleanup ASSUMES the tree is already empty — its canonical producer is GroveDB's own op generation, which emits it only inside the is_empty branch of delete_operation_for_delete_internal (a check that counts same-batch deletes and inserts), with verify_consistency_of_operations covering the window to apply. Documents the misuse consequence (silent, un-tracked orphan + prefix poisoning on re-create), the indexed-primary secondary-sweep exception, and the non-batching path's divergence. Adds a variant comparison table on the enum and a contrast note on DropFlat — the only variant whose contract permits contents. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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In `@grovedb/src/tests/flat_drop_tests.rs`:
- Line 635: Extend the test covering apply_operations_without_batching after the
drop to verify an absence proof for the removed element, add a reference
targeting that element, and assert the expected typed dangling-reference error;
retain existing raw-read and verify_grovedb checks while covering the public
proof and reference-integrity contracts.
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…l typed Closes the two public-contract gaps CodeRabbit flagged on the test suite: an absence proof for the dropped key verifies against the post-drop root hash with an empty result set (with a pre-drop positive proof as sanity), and a reference into the dropped subtree resolves before the drop and returns the typed corrupted-reference error family after it — never stale data. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Implements the O(1) drop of a populated subtree requested by #848, specialized to the case platform actually has (confirmed on the issue discussion): the dropped subtree is declared to contain no child subtrees. That declaration collapses the issue's two-phase detach-and-sweep design — no discovery walk, no sweep queue, no budgeted background pass — because every doomed storage prefix is derivable up front: the subtree's own
blake3(path)prefix plus, for indexed primaries, the three axis secondaries atblake3(prefix ‖ axis_tag). The flatness contract holds by construction for non-Merk data trees and indexed primaries; only a plain Merk tree relies on the caller's word, and a false declaration leaks the children's storage (unreachable, invisible to hashes/proofs/sync/verify) but never corrupts state.Consensus side (GROVE_V4, fail-closed)
GroveDb::drop_flat_subtree(path, key, tx, version)— an ordinary layered delete of the subtree's element from its parent Merk. The child subtree is never opened, so cost is a deterministic function of (element bytes, key, parent shape, path) and independent of the subtree's contents — dropping ten million entries costs the same as dropping ten (pinned by test). Atomically with the delete (sameStorageBatch), one durable redo record is staged into a reserved namespace of the meta column family (unused in production since 2022, outside the root hash), carrying the subtree's full path and the doomed prefixes.SubelementsDeletionBehavior::DropFlaton batchDeleteTreeops — same semantics throughapply_batch/apply_partial_batch/apply_operations_without_batching, classified from the captured actual stored type (the V4 old-value observer), so a declared/stored indexed mismatch cannot slip through. Average/worst-case estimates are extended by the record put's deterministic cost (estimation is replay-critical, and the new behavior only exists under V4, so the estimate lands with the op).operations.flat_drop.{drop_flat_subtree, batch_delete_tree_drop_flat}are0(fail closed) on V1..V3,1on V4, pinned bygrovedb-versiontests.Reclamation (outside consensus, telemetry only)
RocksDbStorage::delete_prefix_ranges— one DB-level range tombstone per (prefix, CF) across all four column families. RocksDB optimistic transactions cannot carryDeleteRange(and the rocksdb crate only implements it for non-transactional write batches), so tombstones are written after the commit: immediately in the same call when GroveDB owns the transaction, otherwise at the host's nextGroveDb::flush_pending_prefix_drops.skipped_live), degrading the violation to a bounded leak instead of destroying live data. The recreate-path test also documents the deeper reason for the contract: stale nodes under the re-derived identical prefix pollute the new tree's namespace, visibly toverify_grovedb.Orphan invisibility (issue requirement 5) — holds by construction
Verified against the actual code paths before designing this: state sync enumerates subtrees by walking the element graph from the root on both source and target, so unreachable prefixes are never requested or shipped;
verify_grovedbrecurses from the root Merk; every iterator is prefix-scoped; the meta CF is outside the root hash, so nodes at different reclamation progress have identical root hashes. RocksDB checkpoints carry both the orphans and the records, so a reopened checkpoint resumes reclamation; a state-synced replica starts orphan-free with an empty queue. Range tombstones are sequence-numbered, so readers holding older snapshots (state-sync sessions, checkpoints) still see pre-drop data.What this deliberately does not do
The issue's fully general two-phase design (drop of subtrees with nested children at any depth, via a persistent sweep queue with budgeted structure discovery) is out of scope here — platform's TTL time-range buckets are flat. The redo-record format and reserved namespace are exactly the bones that design would need (a nested-capable sweep would extend the record with a state machine and cursor), so nothing here paints us into a corner if the general case is ever needed.
Host integration (drive-abci)
DeleteTree(_, DropFlat).flush_pending_prefix_drops(also once at startup, to finish reclamation interrupted by a crash). It is deliberately ungated: a no-op when no records exist, never touches the root hash.Tests
OperationCost), full reclamation incl. all three axis-secondary namespaces for indexed primaries, provable absence + cleanverify_grovedbwhile reclamation is pending, tx atomicity (commit-deferred drain, rollback leaves no record and no tombstones), flush idempotence, simulated crash between tombstones and record removal, recreate-path poisoning (guard skips, fresh data survives, pollution is verify-visible), batch atomicity with sibling ops, fail-closed on GROVE_V3 for both entry points, sum-parent aggregate consistency.Closes #848 for the flat case; if the nested-subtree generalization is still wanted later, I'd suggest a follow-up issue referencing the record format introduced here.
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