Method _startNewExecution

lib/request-handler.js:152–190

* Starts a new execution on the next host of the query plan. * @param {Boolean} [isSpecExec] * @returns {Promise } * @private

(isSpecExec)

   * @private
   */
  async _startNewExecution(isSpecExec) {
    if (isSpecExec) {
      this.client.metrics.onSpeculativeExecution();
    }

    let host;
    let connection;

    try {
      ({ host, connection } = this.getNextConnection());
    } catch (err) {
      return this.handleNoHostAvailable(err, null);
    }

    if (isSpecExec && this._executions.length >= 0 && this._executions[0].wasCancelled()) {
      // This method was called on the next tick and could not be cleared, the previous execution was cancelled so
      // there's no point in launching a new execution.
      return;
    }

    if (this.client.keyspace && this.client.keyspace !== connection.keyspace) {
      try {
        await connection.changeKeyspace(this.client.keyspace);
      } catch (err) {
        this.triedHosts[host.address] = err;
        // The error occurred asynchronously
        // We can blindly re-try to obtain a different host/connection.
        return this._startNewExecution(isSpecExec);
      }
    }

    const execution = new RequestExecution(this, host, connection);
    this._executions.push(execution);
    execution.start();

    if (this.executionOptions.isIdempotent()) {
      this._scheduleSpeculativeExecution(host);
    }
  }

  /**
   * Schedules next speculative execution, if any.