@Override
  public void start() {
    logger.info("BlockingChannelConnectionPool started");
  }
A connection pool that uses BlockingChannel as the underlying connection.
It is responsible for all the connection management. It helps to
checkout a new connection, checkin an existing connection that has been
checked out and destroy a connection in the case of an error
ambry-network/src/main/java/com/github/ambry/network/BlockingChannelConnectionPool.java