code: function metricStart(ctx) {
  	ctx.startTime = Date.now();
  	ctx.startHrTime = process.hrtime();
  	ctx.duration = 0;
  
  	if (ctx.metrics) {
  		const payload = generateMetricPayload(ctx);
  		ctx.broker.emit("metrics.trace.span.start", payload);
  	}
  }
docs: Start metrics & send metric event.
  
  @param {Context} ctx
  
  @private