In a typical GraphQL server, each client request results in a separate execution of resolvers and fetching data from the underlying data sources. This can potentially lead to redundant and unnecessary requests, impacting performance and scalability.

One common solution to this problem is to implement request caching, which allows you to cache the results of previous requests and serve them directly from the cache for subsequent identical requests. This can significantly improve response times and reduce network overhead.

Setting up the cache

To get started, we’ll need to set up a cache layer in our GraphQL server. There are several libraries available for request caching, such as lru-cache and node-cache.

Let’s assume we’re using the lru-cache library. First, install the library using npm:

npm install lru-cache

Next, import the library and create an instance of the cache in your server setup:

const LRU = require('lru-cache');

const cache = new LRU({
  max: 100, // Maximum number of entries to store
  maxAge: 60 * 1000, // Maximum age of each entry (in milliseconds)
});

Wrapping resolvers with caching logic

The next step is to wrap your resolvers with caching logic. This means that before executing a resolver, you’ll first check the cache for a matching result. If found, you can return the cached result and skip the execution of the resolver.

Here’s an example of how you can wrap a resolver with caching logic:

const { graphql, buildSchema } = require('graphql');

const schema = buildSchema(`
  type Query {
    getUser(id: ID!): User
  }

  type User {
    id: ID!
    name: String
    email: String
  }
`);

const getUserResolver = async (args) => {
  const { id } = args;

  // Check cache for a matching result
  const cachedResult = cache.get(id);
  if (cachedResult) {
    return cachedResult;
  }

  // Perform actual data fetching
  const user = await fetchUserFromDataSource(id);

  // Cache the result
  cache.set(id, user);

  return user;
};

const root = {
  getUser: getUserResolver,
};

const query = `
  query GetUser($id: ID!) {
    getUser(id: $id) {
      id
      name
      email
    }
  }
`;

const executeQueryWithCache = async (query, variables) => {
  const result = await graphql(schema, query, root, null, variables);
  return result;
};

executeQueryWithCache(query, { id: '123' })
  .then((result) => {
    console.log(result);
  })
  .catch((error) => {
    console.error(error);
  });

In this example, we have a getUser resolver that first checks the cache for a matching result using the id argument. If a result is found, it is returned directly from the cache. Otherwise, the resolver fetches the user from the underlying data source, caches the result, and returns it.

Clearing the cache

Sometimes, you may need to clear the cache to ensure fresh data is fetched for subsequent requests. This can be done by calling the reset method of the cache instance:

cache.reset();

You can trigger this cache reset whenever relevant data changes or at specified intervals to keep the cache up-to-date.

#graphql #caching