code: protected String invokeServiceProcess(Long processId, Long eventInstId, String masterRequestId,
              String masterRequest, Map<String,Object> parameters, String responseVarName,
              int performanceLevel, Map<String,String> headers) throws Exception {
          Map<String,String> stringParams = translateParameters(processId, parameters);
          ProcessEngineDriver engineDriver = new ProcessEngineDriver();
          return engineDriver.invokeService(processId, OwnerType.DOCUMENT, eventInstId, masterRequestId,
                  masterRequest, stringParams, responseVarName, performanceLevel, null, null, headers);
      }
docs: Invoke a service (synchronous) process. The method cannot be used
  if the process is not a service process.
  Performance level:
  0 - to be determined by property, which will set the level to one of the following
  1,3,5,7,9 - use asynchronous engine  (9 not implemented: 9=7
  2,4,6,8,10 - use synchronous engine
  9,10 - use single transaction
  7,8,9,10 - all cache options CACHE_ONLY
  5,6 - CACHE_OFF for activity/transition, CACHE_ONLY for variable/document
  3,4 - CACHE_OFF for activity/transition, CACHE_ON for variable/document
  1,2 - all cache options CACHE_OFF
  Defaults:
  a. if PROP_DO_PARTIAL_DB_LOGGING property is specified:
  - use 6 if its value is true
  - use 10 otherwise (the property is specified but value is not true)
  b. if MDW_PERFORMANCE_LEVEL_SERVICE is specified
  - use that value
  c. use 3.
  For additional information, see javadoc for ProcessEngineDriver:invokeService
  
  @param process the process definition. You can use {@link #getProcessDefinition(Long)}
  to retrieve the process definition from a process ID.
  @param eventInstId external event instance ID
  @param masterRequestId master request ID
  @param masterRequest the request content
  @param parameters Input parameter bindings for the process instance to be created
  @param responseVarName optional response variable (otherwise implicit "response" is used)
  @param performanceLevel
  @param headers requestHeaders
  @return response message, which is obtained from the response variable