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[Fusion] Skip lookups for entities the request already fetched - #10606
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michaelstaib merged 8 commits intoOct 19, 2026
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…hem up again A lookup now takes an entity from the composite result when a node it depends on already wrote the same entity (same lookup type and requirement values) with every leaf field the lookup selects. The target rows point at the existing values, so no value data is copied, and a lookup whose entities are all served completes without a source schema request. On the graphql-federation-benchmarks query this removes the products and accounts lookups of the third wave, so the inventory lookup starts one wave earlier (4 -> 3 sequential source schema requests, 6 -> 4 requests per gateway request). Reuse is limited to query plans without incremental delivery, lookups without forwarded variables, simple requirements and leaf selections, and producers whose fields are written only by transitive dependencies of the lookup. It can be turned off with FusionOptions.EnableEntityReuse.
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The entity reuse index is created once when the operation plan is constructed and stored in the operation features, which are unique per plan. The plan exposes it through an extension property, and lookups read their reuse by id from an array instead of a reference-keyed dictionary behind a weak table. The analysis now parses the plan's operation text with trusted parser options and resolves dependencies through the plan's own nodes, so a plan it cannot analyze gets no reuse instead of failing.
A producer entity is only reused when its key selection is the requirement field itself, with the same field definition and arguments as at every lookup target. An alias such as `id: username` no longer turns another field into the entity key. Entities are no longer reused while the result holds errors, so a field that returns a value together with an error keeps that error at every position the lookup fills. The reuse analysis no longer fails planning: a plan it cannot analyze executes without entity reuse.
EntityReuse becomes EntityReuseCandidateList and EntityReuseIndex becomes EntityReuseCandidateMap. The map returns a lookup's list through GetCandidates, the plan exposes it as EntityReuseCandidateMap, and the context through GetEntityReuseCandidates. No behavior changes.
A key whose components are all null does not identify an entity, so entities whose key fields are all null no longer serve as reuse candidates. Composite keys with some null components stay reusable.
Each lookup target scanned every candidate, which is quadratic when nothing is reused. Above four candidates, targets now probe the dedup table that already indexes the candidate variables. EntityReuseCandidateMatchingBenchmark measures the crossover between the scan and the probe.
Lookups whose key has nested fields get no reuse candidates and always fetch.
This was referenced Oct 21, 2026
This was referenced Oct 25, 2026
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