Execution getExecutionForFunctionOnRegionWithFilter(Set<String> sessionIds) {
    return FunctionService.onRegion(getSessionRegion()).withFilter(sessionIds);
  }
For peer-to-peer the backing cache *is* what's embedded in tomcat so it's always available

@return boolean indicating whether a backing cache is available
extensions/geode-modules/src/main/java/org/apache/geode/modules/session/catalina/PeerToPeerSessionCache.java