graphql-performance

# GraphQL Performance

Apply GraphQL performance optimization techniques to create efficient,
scalable APIs. This skill covers query complexity analysis, depth
limiting, batching and caching strategies, DataLoader optimization,
monitoring, tracing, and database query optimization.

## Query Complexity Analysis

Query complexity analysis prevents expensive queries from overwhelming
your server by calculating and limiting the computational cost.

```typescript
import { GraphQLError } from 'graphql';
import { ApolloServer } from '@apollo/server';

// Complexity calculator
const getComplexity = (field, childComplexity, args) => {
  // Base complexity for field
  let complexity = 1;

  // List multiplier based on limit argument
  if (args.limit) {
    complexity = args.limit;
  } else if (args.first) {
    complexity = args.first;
  }

  // Add child complexity
  return complexity + childComplexity;
};

// Directive-based complexity
const schema = `
  directive @complexity(
    value: Int!
    multipliers: [String!]
  ) on FIELD_DEFINITION

  type Query {
    user(id: ID!): User @complexity(value: 1)
    users(limit: Int): [User!]! @complexity(
      value: 1,
      multipliers: ["limit"]
    )
    posts(first: Int): [Post!]! @complexity(
      value: 5,
      multipliers: ["first"]
    )
  }

  type User {
    id: ID!
    posts: [Post!]! @complexity(value: 10)
  }
`;

// Complexity validation plugin
const complexityPlugin = {
  requestDidStart: () => ({
    async didResolveOperation({ request, document, operationName }) {
      const complexity = calculateComplexity({
        document,
        operationName,
        variables: request.variables
      });

      const maxComplexity = 1000;

      if (complexity > maxComplexity) {
        throw new GraphQLError(
          `Query is too complex: ${complexity}. ` +
          `Maximum allowed: ${maxComplexity}`,
          {
            extensions: {
              code: 'QUERY_TOO_COMPLEX',
              complexity,