@Override
  public void postOpen(ObserverContext<? extends RegionCoprocessorEnvironment> c) {
    RegionCoprocessorEnvironment env = c.getEnvironment();
    Configuration conf = env.getConfiguration();
    sleepTime.set(conf.getLong(SLEEP_TIME_CONF_KEY, DEFAULT_SLEEP_TIME));
  }
This coproceesor sleep 2s at first increment/append rpc call.
hbase-server/src/test/java/org/apache/hadoop/hbase/client/SleepAtFirstRpcCall.java