protected void createCompactionPolicy(Configuration conf, HStore store) throws IOException {
    String className =
      conf.get(DEFAULT_COMPACTION_POLICY_CLASS_KEY, DEFAULT_COMPACTION_POLICY_CLASS.getName());
    try {
      compactionPolicy = ReflectionUtils.instantiateWithCustomCtor(className,
        new Class[] { Configuration.class, StoreConfigInformation.class },
        new Object[] { conf, store });
    } catch (Exception e) {
      throw new IOException("Unable to load configured compaction policy '" + className + "'", e);
    }
  }
Default StoreEngine creates the default compactor, policy, and store file manager, or their
derivatives.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/DefaultStoreEngine.java