packages/data-point-service/lib/redis-controller.js
function setSWRStaleEntry (service, key, value, ttl) {
  return setEntry(service, createSWRStaleKey(key), value, ttl)
}
function setSWRStaleEntry (service, key, value, ttl) {
  return setEntry(service, createSWRStaleKey(key), value, ttl)
}
function setSWRStaleEntry ( service , key , value , ttl ) { return setEntry ( service , createSWRStaleKey ( key ) , value , ttl ) }
When stale is provided the value is calculated as ttl + stale
@param {Service} service Service instance
@param {String} key entry key
@param {Object} value entry value
@param {Number|String} ttl time to live value supported by https://github.com/zeit/ms
@returns {Promise}
When stale is provided the value is calculated as ttl + stale