Metrics that help measure connection saturation and roundtrip latency

[gkawamoto]

Includes four new metrics:

• beanstalk_client_command_roundtrip_latency to measure the time between the command being sent and the response arriving to the client.
• beanstalk_client_command_count to measure the number of commands sent to beanstalkd.
• beanstalk_client_command_error_count to measure the number of errors returned from the commands sent to beanstalkd.
• beanstalk_client_command_queue_latency to measure the time between acquiring the lock to execute commands.

Those metrics were added via opencensus and can views that bound to them can be accessed via the beanstalk.MetricViews method in stats.go

Example:

package main 

import (
	"github.com/prep/beanstalk"
	"go.opencensus.io/stats/view"
)

func main() {
	err := view.Register(beanstalk.MetricViews()...)
	 if err != nil {
		panic(err)
	}
	// ... your code
}