twitter-algorithm/graph-feature-service/doc/getintersection.md

# GetIntersection

## Request and response syntax

A `GetIntersection` call takes as input a `GfsIntersectionRequest` thrift struct. 

```thrift
struct GfsIntersectionRequest {
  1: required i64 userId
  2: required list<i64> candidateUserIds
  3: required list<FeatureType> featureTypes
}
```

The response is returned in a `GfsIntersectionResponse` thrift struct.

```thrift
struct GfsIntersectionResponse {
  1: required i64 userId
  2: required list<GfsIntersectionResult> results
}

struct GfsIntersectionResult {
  1: required i64 candidateUserId
  2: required list<IntersectionValue> intersectionValues
}

struct IntersectionValue {
  1: required FeatureType featureType
  2: optional i32 count
  3: optional list<i64> intersectionIds
  4: optional i32 leftNodeDegree
  5: optional i32 rightNodeDegree
}(persisted="true")
```

## Behavior

The `GfsIntersectionResponse` contains in its `results` field a `GfsIntersectionResult` for every candidate in `candidateIds` which contains an  `IntersectionValue` for every `FeatureType` in the request's `featureTypes` field. 

The `IntersectionValue` contains the size of the intersection between the `leftEdgeType` edges from `userId` and the `rightEdgeType` edges from `candidateId` in the `count` field, as well as their respective degrees in the graphs in `leftNodeDegree` and `rightNodeDegree` respectively.

**Note:** the `intersectionIds` field currently only contains `Nil`.