@Test
  public void testOnConfigurationChange() {
    PrefetchExecutorNotifier prefetchExecutorNotifier = new PrefetchExecutorNotifier(conf);
    conf.setInt(PREFETCH_DELAY, 40000);
    prefetchExecutorNotifier.onConfigurationChange(conf);
    assertEquals(prefetchExecutorNotifier.getPrefetchDelay(), 40000);

    // restore
    conf.setInt(PREFETCH_DELAY, 30000);
    prefetchExecutorNotifier.onConfigurationChange(conf);
    assertEquals(prefetchExecutorNotifier.getPrefetchDelay(), 30000);

    conf.setInt(PREFETCH_DELAY, 1000);
    prefetchExecutorNotifier.onConfigurationChange(conf);
  }
Read a storefile in the same manner as a scanner -- using non-positional reads and without
waiting for prefetch to complete.
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestPrefetch.java