bad performance and high memory usage when returning large array of nested objects

This is basically a clone of an issue smallrye/smallrye-graphql#930 which I originally opened in SmallRye GraphQL, but it was suspected to be only relevant to graphql-java.

I encountered a performance issue when returning a large array of nested objects as response to a GraphQL query and was wondering whether it would be considered an actual performance issue or out of scope. Here is a minimal test class to illustrate the issue, using graphql-java 17.3 with java 17:

class GraphQLPerformanceTest {
    private static final List<SomeWrapper> objects = IntStream
            .range(0, 10_000_000)
            .mapToObj(i -> new SomeWrapper("value #" + i))
            .collect(Collectors.toList());

    @Value
    public static class SomeWrapper {
        String someValue;
    }

    private final GraphQL graphQL;

    public GraphQLPerformanceTest() {
        TypeDefinitionRegistry typeDefinitionRegistry = new SchemaParser().parse(
                """
                type Query {
                    giveMeLargeResponse: [SomeWrapper]
                }
                type SomeWrapper {
                    someValue: String
                }
                """
        );
        RuntimeWiring wiring = RuntimeWiring.newRuntimeWiring()
                .type(newTypeWiring("Query")
                        .dataFetcher("giveMeLargeResponse", env -> objects))
                .build();
        GraphQLSchema schema = new SchemaGenerator().makeExecutableSchema(typeDefinitionRegistry, wiring);
        this.graphQL = GraphQL.newGraphQL(schema).build();
    }

    @Test
    void testPerformance() {
        graphQL.execute(
            """
            query {
                giveMeLargeResponse {
                    someValue
                }
            }
            """
        );
    }
}

The request takes roughly 12s to return on my Dell precision 7560 notebook with an Intel(R) Core(TM) i9-11950H CPU @ 2.60GHz and intermittedly takes up over 4GB of RAM.

I know 10 million entries is a lot, but I expected the query to return much faster, given that it only needs to serialize and output the data. The majority of the time seems to be spent within completeValueForList:

The flame graph in IntelliJ looks something like this, so I couldn't see any obvious low hanging fruit:

I attached the intellij profiling data and the visualvm snapshot data:

GraphQLPerformanceTest_testPerformance_2021_11_04_111402.zip
graphql-java-performance-snapshot.zip