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perf(db-ivm): merge equal groupBy contributions by identity, not hash - #2112
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groupBy merges equal contributions to a group, which made the reduce index hash every contribution: about a third of a grouped-count hydrate. Each contribution now leads with an identity string built from its pre-aggregate values, normalized as the structural hash normalizes them (-0 as 0, one NaN) and length-prefixed so adjacent values cannot run together. The reduce index merges equal identities without hashing (Index prefixIdentity). Query group values, route representatives, row metadata and avg declare identities; other objects keep the hash path. The incrementalization oracle gains a string-extrema lane whose value table holds pairs that read alike under a separator-only encoding. It fails a mutant that drops the length prefix, which passed every suite before; a sign-blind number identity, a constant representative identity and a constant metadata identity also fail. Co-authored-by: Isaac <no-reply@databricks.com>
🦋 Changeset detectedLatest commit: 69e17b0 The changes in this PR will be included in the next version bump. This PR includes changesets to release 25 packages
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Incremental update benchmarkComparing Overall median write time vs base: 1.01× · cold hydrate time: 1.02× (geometric mean of per-case ratios; lower is faster). Writes: 3 regression(s), 4 improvement(s) (threshold: ±20% and >0.05ms). Cold hydrate: 1 regression(s), 0 improvement(s) (threshold: ±50% and >5ms). Per-case flags are noisy on shared runners. Read the geometric means first. Writes
Cold hydrate
Each row aggregates the 14.4 scale/index/write-mode configurations of that query; per-configuration tables below. 100 rows/collection | source indexes: none | synced writes — geomean 0.90×, cold 0.90×, 1 change(s)
100 rows/collection | source indexes: none | optimistic writes — geomean 1.08×, cold 1.03×
100 rows/collection | source indexes: manual | synced writes — geomean 1.01×, cold 0.89×
100 rows/collection | source indexes: manual | optimistic writes — geomean 1.00×, cold 1.11×
1,000 rows/collection | source indexes: none | synced writes — geomean 1.06×, cold 0.99×, 1 change(s)
1,000 rows/collection | source indexes: none | optimistic writes — geomean 0.97×, cold 0.96×
1,000 rows/collection | source indexes: manual | synced writes — geomean 1.05×, cold 1.04×
1,000 rows/collection | source indexes: manual | optimistic writes — geomean 0.97×, cold 1.00×
10,000 rows/collection | source indexes: none | synced writes — geomean 0.92×, cold 1.02×, 3 change(s)
10,000 rows/collection | source indexes: none | optimistic writes — geomean 1.00×, cold 0.94×
10,000 rows/collection | source indexes: manual | synced writes — geomean 1.11×, cold 1.84×, 2 change(s)
10,000 rows/collection | source indexes: manual | optimistic writes — geomean 1.11×, cold 0.79×, 1 change(s)
Runner: node v24.8.0, linux 6.17.0-1022-azure, AMD EPYC 7763 64-Core Processor. Timings on shared CI runners are noisy; treat small deltas as indicative only. |
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Docstring coverage is 65.22% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 9 files. (2 skipped: … | Write docstrings for the functions missing them to satisfy the coverage threshold. |
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Check name Status Explanation Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request. Title check The title clearly and concisely describes the main change: merging equal groupBy contributions by identity instead of hash. Description check The description includes all required sections, explains the motivation and implementation, reports validation results, confirms local testing, and documents the generated changeset.
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Docstring coverage is 65.22% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 9 files. (2 skipped: 2 unsupported.)
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… its oracle gaps Group keys that serialize alike but hash apart (Maps in a different insertion order) merged their contributions, and a group could then report a deleted row's key. The group key is now part of the identity; a key without one sends the contribution to the hash path. A focused witness fails on the previous commit and passes now; it passes on main. Dense arrays of primitives get identities, so min and max inputs no longer fall back to hashing (a grouped min hydrates 2.2x faster than main). avg reuses identityPart. The reduce callback reads contributions in place and reuses the hoisted aggregate entries. The Index refinement oracle runs every history with prefixIdentity too; merging unprefixed values or ignoring the option in a prefix map fails. The incrementalization law gains a mean-alone lane, which fails a constant avg identity. The changeset no longer overclaims the law. Co-authored-by: Isaac <no-reply@databricks.com>
The mangle-cache safety check reads every identifier-like token in db
and db-ivm source, string literals included, so the tags `l` and `a${`
collided with two short names in the cache. Punctuation tags keep the
same self-delimiting encoding and never read as identifiers.
Co-authored-by: Isaac <no-reply@databricks.com>
Index is not exported from @tanstack/db-ivm. Co-authored-by: Isaac <no-reply@databricks.com>
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Review comments at @.changeset/perf-group-contribution-identity.md:
- Line 8: Update the custom-identity description in the changeset to state that
inputs sharing the same non-undefined identity must also be equal under
structural hashing, while preserving the existing hash-equal input requirement.
Keep this consistent with the ReduceOptions contract in reduce.ts.
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…patch groupBy decided whether a value had an identity from facts the hash does not read: it rejected array subclasses, class-instance keys and non-enumerable symbols. A retraction holding an equal array subclass then landed under no prefix while its insert had one, so they never cancelled and min kept the deleted value. hash.ts now exports structuralIdentity, built on objectParts and enumerable keys like the hash, and groupBy uses it for values and group keys. A groupBy witness fails on the previous head and passes now. A structural identity oracle checks agreement with equalHashValues over equal representations and independent values; four mutants fail it. avg's identity drops its constant count. The reduce option is internal, and the changeset states the identity hook's two-way contract. Co-authored-by: Isaac <no-reply@databricks.com>
Move the contribution encoder into hash.ts as structuralIdentity so it reads exactly what equalHashValues reads: the objectParts marker and headers and the enumerable own keys. Dates, RegExps, Maps, Sets and Uint8Arrays now get an identity; a NaN header or an enumerable symbol key gets none. Remove the per-aggregate identity hook and the compiler's representative and metadata identities, which the generic encoder now covers. Rewrite the structural identity oracle around an independent normal-form model, with separator-bearing strings and keys, pinned collision pairs and a cyclic witness. Update the incrementalization lane's text pairs for the new string encoding. Co-authored-by: Isaac <no-reply@databricks.com>
…on-identity # Conflicts: # packages/db-ivm/src/hashing/hash.ts
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🎯 Changes
Aggregate queries hydrate and update faster.
groupBymerges equal contributions to a group, so that a count change does not read the whole group again (#2081). To find equal contributions, the reduce index hashed every contribution. Since #1797, each contribution holds representatives and row metadata, so the hash input became larger. In a grouped count over a 10,000-row join, hashing was about a third of the hydrate.Each contribution now leads with an identity string that
groupBybuilds from its pre-aggregate values. The reduce index uses the newprefixIdentityoption, so it merges contributions with equal identities without hashing them.The identity law
Two contributions to one group get equal identities exactly when D2 value identity (
equalHashValues) treats them as equal. So the index merges the same contributions as before.structuralIdentity). It reads only whatequalHashValuesreads: the type, theobjectPartsmarker and headers, and the enumerable own keys.-0as0, and everyNaNas one value. Strings and object keys are length-prefixed, so adjacent values cannot run together.undefined. An array subclass, a class instance or a null-prototype object gets the identity of its plain equivalent. The hash treats them the same way.NaNheader, such as an invalid Date or a RegExp whoselastIndexisNaN.equalHashValuescompares headers with===, so such a value equals nothing.Results
Rindle benchmark, 10,000 issues,
NODE_ENV=production, median of 3 interleaved runs againstmain:A direct probe used 10,000 rows in 500 groups. A grouped
minhydrates in 25 ms (main: 56 ms). A groupedcounthydrates in 16 ms (main: 38 ms).Evidence
equalHashValueson every pair.main's hash-basedgroupBy. A mean-alone lane also runsavgwith no other aggregate.prefixIdentitytoo. Two mutants fail it: one merges unprefixed values, and one ignores the option in a prefix map.@tanstack/db-ivm: 697 tests pass.@tanstack/db: 12,074 tests pass, with no type errors. The mangle cache check passes.minormax.✅ Checklist
pnpm test.🚀 Release Impact
This pull request and its description were written by Isaac.