feat: merge a limited path query below a key another branch already owns by QuantumExplorer · Pull Request #850 · dashpay/grovedb

QuantumExplorer · 2026-09-04T18:07:05Z

Issue being fixed or feature implemented

PathQuery::merge (v1, GROVE_V4+) grafts a limited input exclusively at the first key past the common path and refuses any collision there. That refuses compositions whose inputs merely share that key and diverge right below it:

a limited page on post (an index range, […, post, hashtag]) merged with an unlimited by-id fetch on post ([…, post, 0]): both graft at key post;
once a third input in another contract lifts the common path up to the root, a limited page and a limited lookup under the same contract graft at the contract-id key.

Budgets never blend in these shapes; the merge just stopped one level too early. Platform's composite document queries (a page plus derived joins / lookups / counts under one proof) hit both cases immediately.

The collision, before this PR

Two inputs under contract C. The by-id fetch has no limit and goes through the full merge machinery first, so it owns key post as a conditional branch. The page carries a limit, so it may only graft on an exclusive key. Its first key past the common path is post again, and the merge refused it there even though the two only share that one key.

flowchart TD
    subgraph inputs["inputs, common path = [C]"]
        A["A  page<br/>[C, post, hashtag]<br/>limit 20"]
        B["B  by-id fetch<br/>[C, post, 0]<br/>no limit"]
    end
    R(["merged root at [C]"])
    B -- "limit-free: merged first" --> R
    R -- "key post (conditional branch)" --> P["post"]
    P -- "0" --> B2["B's body: the ids"]
    A -. "limited: needs an exclusive key,<br/>but post is already owned" .-> P
    P -. "before: NotSupported" .-> X["refused"]
    style X fill:#fdd,stroke:#c33,color:#600

What was done?

A limited branch colliding on a key that an earlier graft already owns now descends into it (graft_below): both branches are rebuilt as path queries rooted at common_path + [key] and merged with the very same rules, so they either land on exclusive keys of their own or are refused exactly as before (a body meeting the descended root, or a key selected by a range or by the merged root's own items, where nothing below can be told apart). Lifted limits already sit on the leaf bodies as per-instance caps, so the descent lifts nothing twice, and the existing partition (limit-free grafts first, limited grafts last) keeps acceptance independent of input order.

"Owns" follows execution: a key takes the first conditional branch whose selector contains it, in insertion order. So the descent happens only when the merged root selects the key exactly, the first conditional matching it is that exact key, and no range selects it. A conditional shadowed by an earlier range, or one defined for a key the root never selects, would never run, and grafting below it would silently drop the incoming rows, so those shapes refuse instead.

The descent

The owning branch and the incoming branch become two path queries rooted one level down, at [C, post], and go through merge_v1 again. There they diverge onto hashtag and 0, so each lands on an exclusive key of its own. The merged branch replaces the one that owned post.

flowchart TD
    R(["merged root at [C]"])
    R -- "key post" --> G["graft_below<br/>= merge_v1 rooted at [C, post]"]
    G -- "hashtag (exclusive)" --> A2["A's body<br/>per-instance cap 20<br/>(the lifted limit)"]
    G -- "0 (exclusive)" --> B2["B's body<br/>the ids, no cap"]
    style G fill:#e8f4ff,stroke:#369

Because the descent is the same merge, it recurses on its own: if the two still collide on the next key, that key's owner descends again, until the branches diverge or a refusal rule fires.

Where each limited input goes now

flowchart TD
    S["limited input<br/>(global limit or branch caps)"] --> Q1{"path == common path?<br/>(lands at the merged root)"}
    Q1 -- yes --> Q2{"global limit, or a cap<br/>on the root body itself?"}
    Q2 -- yes --> X1["refused:<br/>budget would blend at the root"]
    Q2 -- "no (caps only on its branches)" --> Q3{"other bodies at the root too?"}
    Q3 -- yes --> X2["refused:<br/>a branch cap would govern<br/>rows the other bodies select"]
    Q3 -- no --> OK1["accepted: it IS the root body,<br/>caps ride along"]
    Q1 -- no --> K["first key K past the common path"]
    K --> Q4{"root selects K exactly,<br/>the first conditional matching K<br/>is that exact key,<br/>and no range selects K?"}
    Q4 -- yes --> D["graft_below:<br/>rebuild both at common + [K],<br/>merge_v1 again"]
    D --> Q5{"branches diverge below K?"}
    Q5 -- yes --> OK2["accepted: exclusive keys<br/>one level down"]
    Q5 -- no --> X3["refused:<br/>bodies would meet"]
    Q4 -- no --> Q6{"K selected by the root,<br/>inside a range, or matched<br/>by any conditional?"}
    Q6 -- yes --> X4["refused:<br/>nothing below can be told apart"]
    Q6 -- no --> OK3["accepted: exclusive graft at K<br/>(unchanged from before)"]
    style X1 fill:#fdd,stroke:#c33,color:#600
    style X2 fill:#fdd,stroke:#c33,color:#600
    style X3 fill:#fdd,stroke:#c33,color:#600
    style X4 fill:#fdd,stroke:#c33,color:#600
    style OK1 fill:#dfd,stroke:#393,color:#040
    style OK2 fill:#dfd,stroke:#393,color:#040
    style OK3 fill:#dfd,stroke:#393,color:#040

The root-landing rule is the one refinement outside graft_below: it used to refuse any root-lander carrying any limit. A root-lander whose caps sit on its own branches is now accepted when it is the sole body at the root. That is exactly how a branch merged one level down comes back through graft_below: the rebuilt path query for the owning branch lands at the descended root carrying the caps its leaves already had. Once the root body carries caps, a limit-free branch also takes the exclusive-graft path rather than the full merge machinery (whose instance-limit gate would otherwise refuse it), so an unlimited sibling beside a capped root body merges.

The multi-contract case (a composite proof)

Three inputs: a limited page under contract C1, a limit-free per-post count under C1, and a limit-free profile lookup under contract C2. The common path is the tree root, so C1 is the first key for two of them. The two limit-free inputs graft first and own C1 and C2; the page then descends into C1, where post and like diverge.

flowchart TD
    R(["merged root"])
    R -- "C1" --> C1["graft_below at [C1]"]
    R -- "C2" --> C2["C2"]
    C1 -- "post" --> P["post"]
    P -- "hashtag" --> PH["page body<br/>cap 20"]
    C1 -- "like" --> L["like"]
    L -- "byPost" --> LC["count trees<br/>no cap"]
    C2 -- "profile" --> PR["profile"]
    PR -- "owner" --> PO["profile body<br/>no cap"]
    style C1 fill:#e8f4ff,stroke:#369

Still refused

Same shapes, same answers as before, now reached one level down:

two limited bodies that never diverge (both end at the same leaf: the descended merge finds two root-landers with caps);
a limited body meeting a limit-free one at the same leaf (a cap would govern rows the other body selects);
a key selected by a range rather than an exact key (rows under it cannot be attributed to one branch);
a key whose first matching conditional is an earlier range (the exact-key branch is shadowed and never runs);
a key the root defines a conditional for but never selects (a dormant branch; descending would drop the incoming rows, selecting it would add rows the root never asked for).

No wire or version change: the merge slot is unchanged, the verifier re-runs the same merge, and every previously accepted merge produces the identical query.

How Has This Been Tested?

New tests in per_instance_limit_tests:

merge_grafts_a_limited_branch_below_a_key_a_limit_free_branch_owns: proves, verifies and matches the trusted read; input-order independent
merge_grafts_two_limited_branches_that_diverge_below_a_shared_key: same, with both branches limited
merge_still_refuses_limited_branches_that_never_diverge: two limited bodies at one leaf, a limited body meeting a limit-free one, and a range-selected key all still refuse
merge_refuses_a_limited_graft_shadowed_by_a_range_conditional and merge_refuses_a_limited_graft_into_an_unselected_conditional: the two ownership refusals above, both input orders
merge_grafts_below_an_exact_conditional_before_a_matching_range: an exact conditional ahead of a matching range does own the key; proves and verifies
merge_grafts_an_unlimited_sibling_beside_a_root_branch_cap: both directions, conditional and default subquery; proves and verifies
merge_nested_limited_grafts_is_independent_of_all_input_permutations: a two-level shared prefix plus an unrelated root tree, every input permutation; identical merged query, identical read to the concatenated trusted reads, proves and verifies

Existing merge / per-instance-limit / merge-versioning suites unchanged and green; cargo clippy -p grovedb --all-features -- -D warnings clean; verify-only build OK.

🤖 Generated with Claude Code

Summary by CodeRabbit

Improvements
- Query merging now supports limited branches that share an exact key but diverge beneath it.
- Each limited branch preserves its own result limit during merging.
- Merging remains rejected when branches do not diverge or when the shared key is selected by a range.
Tests
- Added coverage for compatible limited-branch merges and cases that must continue to be rejected.

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grovedb/src/tests/per_instance_limit_tests.rs

📝 Walkthrough

Walkthrough

The merge logic now grafts limited branches below diverging exact-key branches. It preserves rejection for range-selected keys, merged-root items, and branches that do not diverge. Tests cover limits, proofs, order independence, and rejected cases.

Changes

Limited branch grafting

Layer / File(s)	Summary
Root handling and merge contracts `grovedb/src/query/merge/mod.rs`, `grovedb/src/query/merge/v1.rs`	Root-landing inputs now allow branch caps while rejecting unsupported limited root-body combinations. Documentation describes exact-key descent and rejected overlaps.
Merge grafting logic `grovedb/src/query/merge/v1.rs`	Limited and unlimited branches use one merge path. `graft_below` merges path queries with `merge_v1` and reconstructs the merged branch. Unsupported collisions still return errors.
Merge graft validation `grovedb/src/tests/per_instance_limit_tests.rs`	Tests cover grafting below limited and limit-free branches, per-instance limits, proof verification, input-order independence, and rejected collisions.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: 🔵 Low · up to 9a452

Nested limited-branch merges may produce incorrect query results or proofs despite being order-independent. Add nested execution and proof coverage before relying on this behavior broadly.

Sequence Diagram(s)

sequenceDiagram
  participant PathQuery
  participant graft_below
  participant merge_v1
  PathQuery->>graft_below: graft a branch below an exact key
  graft_below->>merge_v1: merge path queries rooted below the key
  merge_v1-->>graft_below: return merged query
  graft_below-->>PathQuery: reconstruct the merged branch

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 3 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: merging a limited path query below a key already owned by another branch.

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…a shared key, #850) Pins grovedb at dashpay/grovedb#850: `PathQuery::merge` (v1) now descends into a key another grafted branch already owns and grafts a limited branch where the two actually diverge, instead of refusing the collision at the first key past the common path; a lone body landing at a merged root keeps the caps on its own branches. Composite document queries (a page plus derived sub-queries under one merged proof) need this: a limited page on `post` merged with a by-id fetch on `post`, or a limited page and a limited lookup under one contract once a cross-contract sub-query lifts the common path to the root, all collide one level above where they diverge. Also carries #849 (flat-subtree drop) from develop. No API change on the platform side. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

`PathQuery::merge` (v1) grafts a limited input exclusively at the first key past the common path and refuses any collision there. That refuses compositions whose inputs only SHARE that key and diverge right below it: a limited page on `post` merged with an unlimited by-id fetch on `post`, or, once a third input lifts the common path up to the root, a limited page and a limited lookup under the same contract key. The budgets never blend in those shapes; the merge just stopped one level too early. A limited branch colliding on a key an earlier graft owns now descends into it: both branches are rebuilt as path queries rooted at `common_path + [key]` and merged with the same rules, so they either land on exclusive keys of their own or are refused exactly as before (a body meeting the descended root, a key selected by a range or by the merged root's own items). Lifted limits already sit on the leaf bodies as instance caps, so the descent lifts nothing twice, and the partition (limit-free grafts first) keeps acceptance independent of input order. Tests: a limited branch grafts below a key a limit-free branch owns, two limited branches graft where they diverge (both prove, verify and match the trusted read, in every input order), and the refusals hold for branches that never diverge. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

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Inline comments:
In `@grovedb/src/query/merge/v1.rs`:
- Around line 307-310: The SubqueryBranch conversion around subquery_path loses
the nested path for flattened branches that still contain instance limits,
making merge_v1 order-dependent. Preserve the remaining nested path and avoid
representing such limited branches as root-landing bodies, using the existing
branch/limit metadata in the surrounding merge logic. Add a permutation
regression test covering docs/p2, docs/p1/a, docs/p1/b, and an unrelated root
path in both processing orders.

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…a shared key, #850) Pins grovedb at dashpay/grovedb#850: `PathQuery::merge` (v1) now descends into a key another grafted branch already owns and grafts a limited branch where the two actually diverge, instead of refusing the collision at the first key past the common path; a lone body landing at a merged root keeps the caps on its own branches. Composite document queries (a page plus derived sub-queries under one merged proof) need this: a limited page on `post` merged with a by-id fetch on `post`, or a limited page and a limited lookup under one contract once a cross-contract sub-query lifts the common path to the root, all collide one level above where they diverge. Also carries #849 (flat-subtree drop) from develop. No API change on the platform side. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

codecov · 2026-09-04T18:25:16Z

Codecov Report

❌ Patch coverage is 97.32143% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.58%. Comparing base (d548e28) to head (8d78f06).

Files with missing lines	Patch %	Lines
grovedb/src/query/merge/v1.rs	97.32%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #850   +/-   ##
========================================
  Coverage    92.58%   92.58%           
========================================
  Files          297      297           
  Lines        92199    92283   +84     
========================================
+ Hits         85358    85440   +82     
- Misses        6841     6843    +2

Components	Coverage Δ
grovedb-core	`90.80% <97.32%> (+0.01%)`	⬆️
merk	`93.27% <ø> (ø)`
storage	`91.70% <ø> (ø)`
commitment-tree	`96.38% <ø> (ø)`
mmr	`95.12% <ø> (ø)`
bulk-append-tree	`92.75% <ø> (ø)`
element	`97.98% <ø> (ø)`

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Inline comments:
In `@grovedb/src/tests/per_instance_limit_tests.rs`:
- Around line 1761-1764: Add nested docs/p1/a and docs/p1/b fixtures to the
per-instance limit test, then execute the merged query and compare its result
with concatenated trusted reads. Also invoke assert_proved_matches_trusted_read
for the merged query so nested graft execution and proof behavior are validated,
while retaining the existing permutation-based merge assertions.

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grovedb/src/query/merge/mod.rs
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The permutation test compared merged query structures only, so a merge that was wrong in the same way for every input order would have passed. It now populates the two-level prefix (docs/p1/a, docs/p1/b, docs/p2) and the unrelated root tree, and for every permutation checks that the merged read equals the concatenated trusted reads of the inputs and that the proof verifies to the same rows. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

QuantumExplorer

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QuantumExplorer mentioned this pull request Sep 4, 2026

chore: bump grovedb to 2d95c567 (#850 merged: limited branches graft below a shared key) dashpay/platform#4597

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QuantumExplorer force-pushed the feat/merge-recursive-graft branch from 58bb830 to 8b546f4 Compare September 4, 2026 18:11

QuantumExplorer force-pushed the feat/merge-recursive-graft branch from 8b546f4 to 5b5f4bf Compare September 4, 2026 18:14

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QuantumExplorer mentioned this pull request Sep 4, 2026

feat(drive): composite document queries: a page plus derived sub-queries under one merged proof dashpay/platform#4598

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fix: preserve active branches when merging limited queries

9a45271

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Comment thread grovedb/src/tests/per_instance_limit_tests.rs Outdated

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QuantumExplorer merged commit 2d95c56 into develop Sep 5, 2026
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QuantumExplorer deleted the feat/merge-recursive-graft branch September 5, 2026 03:53

This was referenced Sep 5, 2026

fix: synthesized split bodies walk in the merged branches' direction #851

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feat(sdk): composite document queries, the client stack dashpay/platform#4604

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feat(wasm-sdk): composite document queries on the JS surface dashpay/platform#4605

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feat: merge a limited path query below a key another branch already owns - #850

feat: merge a limited path query below a key another branch already owns#850
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QuantumExplorer commented Sep 4, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Issue being fixed or feature implemented

The collision, before this PR

What was done?

The descent

Where each limited input goes now

The multi-contract case (a composite proof)

Still refused

How Has This Been Tested?

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