Parser caching may be optionally enabled by setting config.graphql.parser_cache = true in your Rails application. The cache may be manually built by assigning GraphQL::Language::Parser.cache = GraphQL::Language::Cache.new("some_dir"). This will create a directory (tmp/cache/graphql by default) that stores a cache of parsed files.
Much like bootsnap, the parser cache needs to be cleaned up manually. You will need to clear the cache directory for each new deployment of your application. Also note that the parser cache will grow as your schema is loaded, so the cache directory must be writable.