private CompletableFuture<Set<ServerName>> getBootstrapNodes() {
    return this
      .<GetBootstrapNodesResponse> call(
        (c, s, d) -> s.getBootstrapNodes(c, GetBootstrapNodesRequest.getDefaultInstance(), d),
        r -> r.getServerNameCount() != 0, "getBootstrapNodes()")
      .thenApply(RpcConnectionRegistry::transformServerNames);
  }
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