@Override
    public Optional<RawConfig> getConfig(RawConfig input, JRTServerConfigRequest request) {
        ConfigKey<?> key = input.getKey();

        Optional<RawConfig> cached = cache.get(new ConfigCacheKey(key, input.getDefMd5()));
        if (cached.isPresent())
            log.log(Level.FINE, () -> "Found config " + key + " in cache");
        return cached;
    }
Retrieves the requested config from the cache. Used when in 'memorycache' mode.

@param request The config to retrieve - can be empty (no payload), or have a valid payload.
@return A Config with a payload.
config-proxy/src/main/java/com/yahoo/vespa/config/proxy/MemoryCacheConfigClient.java