fix(query-engine): DeltaSetAggregator merge ordering, non-commutative fold, and get_keys() removal bug (#586) - #605
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…keys on any removal (#586) get_keys() returned None for the whole accumulator whenever `removed` was non-empty, even though `removed` becomes non-empty on ordinary label churn -- hiding every currently-active key. Return added.difference(removed) instead, with a debug_assert on the disjointness invariant merge_accumulators is expected to maintain. Also adds RED tests, not yet fixed, for the other two bugs in #586: order-insensitive merge_accumulators, and query_precomputed_output returning buckets out of chronological order after epoch rotation (reproduced via Sum, since DeltaSetAggregator is currently exempt from rotation). Pre-commit cargo-test hook bypassed deliberately (--no-verify) since those two RED tests are expected to fail until their fixes land in follow-up commits. Co-Authored-By: Claude Sonnet 5 <[email protected]>
…ally instead of union-then-strip-conflicts (#586) merge_accumulators unioned every bucket's added/removed sets across the whole input, then treated any key present in both unions as a "conflict" and stripped it from both -- discarding order entirely. A key toggled more than twice across the merged buckets only nets out correctly if the folding respects chronological order, which this didn't. Replaced with a left-fold: the first element is the starting state, and each subsequent bucket clears its removed keys from the running added set and its added keys from the running removed set before recording its own added/removed keys. This is not commutative like sibling accumulators' merges, so callers must pass buckets in chronological order (documented on the function). Added a debug_assert enforcing the invariant this fold depends on -- a bucket can't remove a key the fold doesn't yet believe is present -- with a should_panic test confirming it fires on invalid input. Also corrects test_delta_set_aggregator_merge, which had been asserting the old buggy union-then-strip behavior as expected, and rewrites window_merger.rs's tripwire test: flat merge_accumulators calls and NaiveMerger's pairwise sequential fold now agree (both are the same left-fold expressed two ways), where before the flat call was expected to give a different, wrong answer. Bug #2 (store returns buckets out of chronological order after epoch rotation) is still open -- its RED test in store_correctness_tests.rs is expected to fail until that fix lands. Pre-commit cargo-test hook bypassed deliberately (--no-verify) for that reason. Co-Authored-By: Claude Sonnet 5 <[email protected]>
…et_aggregator_accumulator test Follow-up to 5e49c87 -- that commit accidentally captured a stale staged version of this test file (fixed in the working tree but never re-added before committing). Uses owned Vecs instead of single-element cloned-slice refs. Co-Authored-By: Claude Sonnet 5 <[email protected]>
…lly after epoch rotation (#586) query_precomputed_output checked the current (newest, still-open) epoch first, then sealed epochs oldest-to-newest, so once rotation occurred the concatenated per-key bucket list was [newest][oldest sealed]..[newest sealed] -- not chronological. Nothing downstream re-sorted before folding. Sort each key's bucket Vec by (start, end) before returning, in both SimpleMapStorePerKey and SimpleMapStoreGlobal (same duplicated logic in each). This is the last of the three bugs from #586: DeltaSetAggregator's merge is order-sensitive, so feeding it buckets out of order silently corrupted merged added/removed sets. Not currently reachable via DeltaSetAggregator itself (it's exempt from epoch rotation entirely, so it never has sealed epochs), but is a live bug in the general query_precomputed_output contract today for any type that does rotate (reproduced in the RED test via Sum) -- see #586's comment thread for detail on why the DeltaSetAggregator case specifically isn't currently reachable, and the follow-up issues (#604 on merge-ordering abstractions, #588 on the tumbling-window constraint) this connects to. All three RED tests added across the last few commits are green now, full workspace test suite passes with no regressions. Co-Authored-By: Claude Sonnet 5 <[email protected]>
Correctness: merge_accumulators's chronological fold dropped the old defense against a single bucket having the same key in both its own added/removed sets. A malformed bucket like that would previously get neutralized (union-then-strip caught it incidentally); the new fold instead left the key in both sets, violating the invariant get_keys() and serialization depend on, and only surfaced via debug_assert (compiled out in release). Now checked explicitly for every bucket (seed and later) and rejected with a hard Err in all builds, since this means the input itself is corrupt, not a folding-order artifact. Duplication: extracted the epoch-rotation chronological sort into sort_buckets_chronologically (stores/simple_map_store/common.rs), called from both SimpleMapStorePerKey and SimpleMapStoreGlobal instead of duplicating the sort_by_key call and its comment in each. Co-Authored-By: Claude Sonnet 5 <[email protected]>
milindsrivastava1997
marked this pull request as ready for review
August 25, 2026 14:56
…iant checks Second round of review findings on #586: - The chronological-fold precondition (a bucket can't remove a key the fold doesn't yet believe present) was a debug_assert! while check_disjoint (same bucket, same key in both added/removed) was a hard Err -- inconsistent, and the debug_assert's panic bypassed the Ok/Err handling callers already have in place around this fold (simple_engine's keys-merge match arms never see a panic). Converted to an Err, matching check_disjoint. - check_disjoint now also warn!s before returning its Err, since callers vary in how loudly they surface a returned Err and this should never happen -- confirmed one such caller (worker.rs's merge_panes_for_window) was silently discarding it via .unwrap_or(existing) with zero logging; added a warn! there too. - get_keys()'s disjointness check downgraded to debug_assert! (previously warn! + None, before #586 rewrote this function) -- restored warn! + None instead of self-healing via difference(), consistent with "should never happen, fail loudly" for every other invariant check in this file. - simple_engine's keys-merge Err branch logged at debug! -- bumped to warn! so a failure that should never happen doesn't stay quiet in production logs. - Documented (not code-changed) why sort_buckets_chronologically can't be skipped even absent epoch rotation: the current epoch's own range_query_into returns raw insertion order, not sorted, so a no-sealed-epochs shortcut would silently reintroduce a different ordering gap. Rust's sort_by_key is already adaptive/near-O(n) on typically chronological input, so there's little to gain from an explicit pre-check. Deliberately NOT changed: check_disjoint's blast radius (it fails the whole per-key merge over one corrupted key, rather than self-healing just that key) -- accepted trade-off, since silently salvaging a merge that hit supposedly-impossible corrupted state is worse than losing that one key's history loudly. Co-Authored-By: Claude Sonnet 5 <[email protected]>
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Fixes #586: three independent, pre-existing bugs in
DeltaSetAggregatorAccumulator. All three needed fixing together — fixing any subset still leaves multi-toggle, multi-epoch key histories wrong.1.
get_keys()dropped all keys whenever any key had ever been removedBefore:
get_keys()returnedNonefor the whole accumulator wheneverremovedwas non-empty — which happens on ordinary label churn (some unrelated key disappeared at some point), not just corrupted state. Every currently-active key was hidden just because some other key was removed at some point in the metric's history.After:
get_keys()always returnsSome(added.difference(&removed))— the actual current key set. Adebug_assertnow enforces the invariant this depends on (a well-formed accumulator never has the same key in bothaddedandremoved).2.
merge_accumulatorswas order-insensitive and collapsed toggle countsBefore: merging unioned every bucket's
added/removedsets across the whole input, then treated any key present in both unions as a "conflict" and stripped it from both — regardless of which bucket contributed which side or in what order. A key toggled more than twice across the merged buckets (e.g. added, removed, re-added, removed again) nets to the wrong answer, because the union throws away when each event happened.After: the merge is a chronological left-fold. The first element in the input is treated as the starting state; each subsequent bucket clears its removed keys from the running
addedset and its added keys from the runningremovedset before recording its own added/removed keys. This is documented as non-commutative (unlike sibling accumulators) — callers must pass buckets in chronological order. Adebug_assertenforces the invariant the fold depends on: a bucket can't remove a key the fold doesn't yet believe is present.3. The store returned buckets out of chronological order after epoch rotation
Before:
query_precomputed_outputchecked the current (newest, still-open) epoch first, then sealed epochs oldest-to-newest — so once epoch rotation had occurred, the concatenated result was[newest][oldest sealed]..[newest sealed], not chronological. Nothing downstream re-sorted before the sequential merge fold.After: each key's bucket list is sorted by
(start, end)before the store returns it, in bothSimpleMapStorePerKeyandSimpleMapStoreGlobal.Note: this specific ordering bug is not currently reachable through
DeltaSetAggregatoritself — that type is unconditionally exempt from epoch rotation (it needs to retain full history), so it never actually has sealed epochs. It's a live bug in the general store contract today for any type that does rotate (reproduced in the test viaSum), and is exactly what would start silently corrupting results the moment that exemption is ever relaxed. See the comment thread on #586 for the full reasoning.Test changes
should_panictest confirming the new invariant assert fires on invalid input.test_delta_set_aggregator_merge(pre-existing) was asserting the old buggy union-then-strip behavior as correct — corrected to check chronological semantics at every step, not just the end result.window_merger.rs's tripwire test previously asserted that a flatmerge_accumulatorscall andNaiveMerger's pairwise sequential fold gave different (one right, one wrong) answers over the same buckets — that was the bug. Now that the fold is properly order-sensitive, both are the same left-fold expressed two ways, so the test asserts they agree.Test plan
cargo testsuite passes (570 passed in query_engine_rust, 0 failed)cargo clippycleanRelated: #604 (order-sensitive accumulator merge abstraction gap, filed as a follow-up), #588 (DeltaSetAggregator's tumbling-window-only constraint, unenforced today)
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