Issue reproduction

0. Set up the project

yarn install

1. Start the server

yarn start:dev

2. Go to the playground - http://localhost:3000/graphql
3. Run the products query:

query Products {
  products {
    id
    direct
    resolved
    combined
    parent
  }
}

10 000 products will be returned. You can adjust the number in src/products/products.mock.ts file.

Notes about fields:

• id and direct are passed directly from the REST response, no resolver involved
• resolved field is being resolved through a resolver, but a very simple one. Just pointing to the REST field (1:1)
• combined field has a resolver that concatenates two fields (think about it as "full name" that's created from first and last name fields)
• parent same as resolved but uses @Parent() decorator

4. Run the products query with just a single field case to understand its impact

My findings

Methodology

In each case, I run a simple query with id and "a field". Here's the k6 command I used:

k6 run --vus 1 --duration 30s --http-debug ./performance/--CASE--.js

direct

This is the baseline. 1353 requests in 30s:

resolved

resolved field is a 1:1 map to a field (from another service response or database). 582 requests in 30s. That's a 57% degradation in performance! Or in other words, not using a resolver is 2.3x faster.

parent

Same as resolved but also uses @Parent decorator. 346 requests in 30s. That's a ~75% drop in performance! Or in other words, the base is 3.9x faster than a resolver that happens to use the @Parent decorator.

Clinic

I used two cases here, and this time run as many requests as I could in 10 seconds to see if there were any discrepancies in functions being run.

# First terminal
clinic flame -- node ./dist/main.js

# Second terminal
k6 run --vus 1 --duration 10s --http-debug ./performance/direct.js

direct

The hottest function is willResolveField from @apollo.

resolved

This time, the hottest function is in NodeJS - processTicksAndRejections. That indicates a huge amount of asynchronous operations:

parent

Async queue seems to be even busier when using @Parent() decorator:

Working theory

I think that @ResolveField is automatically turning functions into async functions even if the developer didn't state that and is making very simple synchronous operations. In the experiments here, I took it to extreme and just returned the same field to show the difference but a case for simple synchronous operations has to exist.

Think about fullName that concatenates firstName and lastName or renaming some field or any other way of transforming the data.

---

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