Query planner duplicate calls to services on interface types

[delyanr]

Hello,

Packages: apollo-gateway v0.11.6

I'm running a microservice architecture based on the federation specs with apollo-gateway at the helm. One of the microservices defines a BasePost interface type, that is implemented by RegularPost and FeaturedPost, while another microservices defines a User type.

When I run a query to fetch blogs, their posts and authors, I get duplicated calls to the users microservices due to the BasePost interface. See the query planner below:

QueryPlan {
    Sequence {
      Fetch(service: "blogs") {
        {
          blogs {
            id
            posts {
              __typename
              ... on RegularPost {
                id
                author {
                  id
                  __typename
                }
              }
              ... on FeaturedPost {
                id
                author {
                  id
                  __typename
                }
              }
            }
          }
        }
      },
      Parallel {
        Flatten(path: "blogs.@.posts.@.author") {
          Fetch(service: "users") {
            {
              ... on User {
                __typename
                id
              }
            } =>
            {
              ... on User {
                givenName
              }
            }
          },
        },
        Flatten(path: "blogs.@.posts.@.author") {
          Fetch(service: "users") {
            {
              ... on User {
                __typename
                id
              }
            } =>
            {
              ... on User {
                givenName
              }
            }
          },
        },
      },
    },
  }

Given the author has the same fields between the implementing types, I would expect a single Fetch to the users microservice. Is this behaviour normal?

Thanks!

[jazzyray]

Hello,

(Using "@apollo/gateway": "^0.19.1")

Just to add something to this.
Federation over interface objects is virutally unusable for us.

Consider the following federated GraphQL query that sits in front
of three services. Described in this blog post:

https://www.ontotext.com/blog/the-rise-of-the-knowledge-graph

The following graphql query

query {
    annotation(id: "https://www.ontotext.com/blog/the-rise-of-the-knowledge-graph/annotation/1") {
      body {
        source { 
          similar {
           id
           name
          }
        }
        purpose
      }
    }
  }

Returns the attached result and query plan. query-response.txt

The gateway invokes 10s of duplicate backend service queries to the same service with the same set of identical query variables/representations. See log apollo-gw.log

This is a performance nightmare.

Is there any further work (PR's) that might help save me time trying to resolve this.

[abernix]

The fix for this was released in @apollo/gateway@0.27.1! 🎉