@Override
  public void preCompactScannerOpen(ObserverContext<? extends RegionCoprocessorEnvironment> c,
    Store store, ScanType scanType, ScanOptions options, CompactionLifeCycleTracker tracker,
    CompactionRequest request) throws IOException {
    resetTTL(options);
  }
Internal watcher that keep "data" up to date asynchronously.
hbase-examples/src/main/java/org/apache/hadoop/hbase/coprocessor/example/ZooKeeperScanPolicyObserver.java