@Override
    public boolean compact(CompactionContext compaction, HStore store,
      ThroughputController throughputController, User user) throws IOException {
      boolean ret = super.compact(compaction, store, throughputController, user);
      if (ret) compactionStateChangeLatch.countDown();
      return ret;
    }
Don't allow any data to be written out in the compaction by creating a custom
{@link StoreScanner}.
hbase-server/src/test/java/org/apache/hadoop/hbase/coprocessor/TestRegionObserverScannerOpenHook.java