Feature Description

It appears the vttablet transaction throttler has no basic metrics to understand it's operation. This issue is to request the addition of metrics for this throttler.

I have a draft PR ready to implement this

Use Case(s)

The metrics I would like added are:

1. Gauge: TxThrottlerRunning
   • 0 (disabled)
   • 1 (enabled)
2. Counter: TxThrottlerRequests - total # of calls to .Throttle()
3. Counter: TxThrottlerThrottled - total # of throttled calls to .Throttle()

Operation type could be added to the 2 x counters but I'm not sure if it would be useful 🤔

Feedback on more useful metrics appreciated! 🙇