public CountDownLatch getCompactionStateChangeLatch() {
      if (compactionStateChangeLatch == null) {
        compactionStateChangeLatch = new CountDownLatch(1);
      }
      return compactionStateChangeLatch;
    }
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