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fix(federation): fix left-behind selections in fragment reuse #6093

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merged 1 commit into from
Oct 1, 2024

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@goto-bus-stop goto-bus-stop commented Oct 1, 2024

Sometimes, fragment reuse would leave behind a selection in a selection
set that is also part of a fragment that was applied to that selection
set. That's suboptimal.

An example from the Apollo codebase is an output like this:

{
  descendants {
    ...TraceNodeFragment
    errors {
      locations {
        __typename
        line
        column
      }
    }
  }
}
fragment TraceNodeFragment on Trace {
  errors {
    locations {
      __typename
      line
      column
    }
  }
}

Here errors.locations.* is selected twice.

The cause is this difference in our intersection implementation:
https://github.com/apollographql/federation/blob/df5eb3cb0e2b4802fcd425ab9c23714de2707db3/internals-js/src/operations.ts#L2676-L2680

If a field selection's subselection completely disappears in
intersection(), we previously kept the field selection, instead of
removing it entirely.

By returning None we will now correctly remove the duplicate errors selection.


Checklist

Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.

  • Changes are compatible1
  • Documentation2 completed
  • Performance impact assessed and acceptable
  • Tests added and passing3
    • Unit Tests
    • Integration Tests
    • Manual Tests

Exceptions

I did not add a unit test for this as we do not expect to rely on
fragment reuse long-term. Existing tests pass and I manually
tested the problematic Apollo queries.

Footnotes

  1. It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this.

  2. Configuration is an important part of many changes. Where applicable please try to document configuration examples.

  3. Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions.

Sometimes, fragment reuse would leave behind a selection in a selection
set that is also part of a fragment that was applied to that selection
set. That's suboptimal.

An example from the apollo codebase is this:
```graphql
descendants {
  ...TraceNodeFragment
  errors {
    locations {
      __typename
      line
      column
    }
  }
}
fragment TraceNodeFragment on Trace {
  errors {
    locations {
      __typename
      line
      column
    }
  }
}
```

The cause is this difference in our `intersection` implementation:
https://github.com/apollographql/federation/blob/df5eb3cb0e2b4802fcd425ab9c23714de2707db3/internals-js/src/operations.ts#L2676-L2680

If a field selection's subselection completely disappears in
`intersection()`, we previously kept the field selection, instead of
removing it entirely.

By returning `None` we will now correctly remove the duplicate `errors` selection.

I did not add a unit test for this as we do not expect to rely on
fragment reuse long-term.

This comment was marked as resolved.

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router-perf bot commented Oct 1, 2024

CI performance tests

  • connectors-const - Connectors stress test that runs with a constant number of users
  • const - Basic stress test that runs with a constant number of users
  • demand-control-instrumented - A copy of the step test, but with demand control monitoring and metrics enabled
  • demand-control-uninstrumented - A copy of the step test, but with demand control monitoring enabled
  • enhanced-signature - Enhanced signature enabled
  • events - Stress test for events with a lot of users and deduplication ENABLED
  • events_big_cap_high_rate - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity
  • events_big_cap_high_rate_callback - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity using callback mode
  • events_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
  • events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
  • events_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
  • extended-reference-mode - Extended reference mode enabled
  • large-request - Stress test with a 1 MB request payload
  • no-tracing - Basic stress test, no tracing
  • reload - Reload test over a long period of time at a constant rate of users
  • step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
  • step-local-metrics - Field stats that are generated from the router rather than FTV1
  • step-with-prometheus - A copy of the step test with the Prometheus metrics exporter enabled
  • step - Basic stress test that steps up the number of users over time
  • xlarge-request - Stress test with 10 MB request payload
  • xxlarge-request - Stress test with 100 MB request payload

@goto-bus-stop goto-bus-stop merged commit 8401b52 into dev Oct 1, 2024
14 of 15 checks passed
@goto-bus-stop goto-bus-stop deleted the renee/ROUTER-789 branch October 1, 2024 16:01
@duckki
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duckki commented Oct 1, 2024

nice catch!

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3 participants