guides/object_cache/overview.md
GraphQL::Enterprise::ObjectCache is an application-level cache for GraphQL-Ruby servers. It works by storing a {% internal_link "cache fingerprint for each object", "/object_cache/schema_setup#object-fingerprint" %} in a query, then serving a cached response as long as those fingerprints don't change. The cache can also be customized with {% internal_link "TTLs", "/object_cache/caching#ttl" %}.
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:
{{ "/object_cache/query-without-cache.png" | link_to_img:"GraphQL-Ruby profile, without caching" }}
But with ObjectCache, it checks the cache first, returning a cached response if possible:
{{ "/object_cache/query-with-cache.png" | link_to_img:"GraphQL-Ruby profile, with ObjectCache" }}
This reduces latency for clients and reduces the load on your database and application server.
Before running a query, ObjectCache creates a fingerprint for the query using {{ "GraphQL::Query#fingerprint" | api_doc }} and {% internal_link "Schema.context_fingerprint_for(ctx)", "/object_cache/schema_setup#context-fingerprint" %}. 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. Then, it compares the current fingerprint of each object ot the one in the cache and checks .authorized? for that object. If the fingerprints all match and all objects pass authorization checks, then the cached response returned. (Authorization checks can be {% internal_link "disabled", "/object_cache/schema_setup#disabling-reauthorization" %}.)
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.
To get started with the object cache: