lib/errors.js
function BusyConnectionError(address, maxRequestsPerConnection, connectionLength) {
  const message = util.format('All connections to host %s are busy, %d requests are in-flight on %s',
    address, maxRequestsPerConnection, connectionLength === 1 ? 'a single connection': 'each connection');
  DriverError.call(this, message, this.constructor);
  this.info = 'Represents a client-side error indicating that all connections to a certain host have reached ' +
    'the maximum amount of in-flight requests supported (pooling.maxRequestsPerConnection)';
}
function BusyConnectionError(address, maxRequestsPerConnection, connectionLength) {
  const message = util.format('All connections to host %s are busy, %d requests are in-flight on %s',
    address, maxRequestsPerConnection, connectionLength === 1 ? 'a single connection': 'each connection');
  DriverError.call(this, message, this.constructor);
  this.info = 'Represents a client-side error indicating that all connections to a certain host have reached ' +
    'the maximum amount of in-flight requests supported (pooling.maxRequestsPerConnection)';
}
Represents a client-side error indicating that all connections to a certain host have reached
the maximum amount of in-flight requests supported.
@param {String} address
@param {Number} maxRequestsPerConnection
@param {Number} connectionLength
@constructor