GraphQL ObjectCache

GraphQL::Enterprise::ObjectCache is an application-level cache for GraphQL-Ruby servers. It works by storing a cache fingerprint for each object in a query, then serving a cached response as long as those fingerprints don’t change. The cache can also be customized with TTLs.

Why?

ObjectCache can greatly reduce GraphQL response times by serving cached responses when the underlying data for a query hasn’t changed.

Usually, a GraphQL query alternates between data fetching and calling application logic:

But with ObjectCache, it checks the cache first, returning a cached response if possible:

This reduces latency for clients and reduces the load on your database and application server.

How

Before running a query, ObjectCache creates a fingerprint for the query using GraphQL::Query#fingerprint and Schema.context_fingerprint_for(ctx). Then, it checks the backend for a cached response which matches the fingerprint. If a match is found, the ObjectCache fetches the objects previously visited by this query and compares their current fingerprints to the ones in the cache. If the fingerprints all match, then the cached response returned.

If there is no cached response or if the fingerprints don’t match, then the incoming query is re-evaluated. While it’s executed, ObjectCache gathers the IDs and fingerprints of each object it encounters. When the query is done, the result and the new object fingerprints are written to the cache.

Setup

To get started with the object cache:

• Prepare the schema
• Set up a Redis backend or Memcached backend
• Configure types and fields for caching
• Check out the runtime considerations