private String buildConnectionString(Configuration conf) throws UnknownHostException {
    final String configuredBootstrapNodes = conf.get(BOOTSTRAP_NODES);
    if (StringUtils.isBlank(configuredBootstrapNodes)) {
      return MasterRegistry.getConnectionString(conf);
    }
    return Splitter.on(ADDRS_CONF_SEPARATOR).trimResults().splitToStream(configuredBootstrapNodes)
      .collect(Collectors.joining(String.valueOf(ADDRS_CONF_SEPARATOR)));
  }
As end users could configure any nodes in a cluster as the initial bootstrap nodes, it is
possible that different end users will configure the same machine which makes the machine over
load. So we should have a shorter delay for the initial refresh, to let users quickly switch to
the bootstrap nodes we want them to connect to.
<p/>
The default value for initial refresh delay is 1/10 of periodic refresh interval.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/RpcConnectionRegistry.java