private static String toReadWriteStoreKey(SystemStreamPartition ssp, TaskName taskName) {
    Preconditions.checkArgument(ssp != null, "SystemStreamPartition should be defined");
    Preconditions.checkArgument(StringUtils.isNotBlank(ssp.getSystem()), "System should be defined");
    Preconditions.checkArgument(StringUtils.isNotBlank(ssp.getStream()), "Stream should be defined");
    Preconditions.checkArgument(ssp.getPartition() != null, "Partition should be defined");

    String storeKey = ssp.getSystem() + "." + ssp.getStream() + "." + String.valueOf(ssp.getPartition().getPartitionId());
    if (taskName != null) {
      storeKey += "." + taskName.getTaskName();
    }
    return storeKey;
  }
Deletes all fanned out {@link Startpoint}s
samza-core/src/main/java/org/apache/samza/startpoint/StartpointManager.java