prometheus max limit for counters

Question

When using counters in prometheus, would we ever hit the problem of reaching the max limit for the counter (assuming the application never restarts) ? If so, would it affect the underlying application that is trying to expose the metric or would it be taken care by prometheus?

Answer 1

If you take a look at the declaration of counter metrics type from prometheus/client_golang.

type counter struct {
    // valBits contains the bits of the represented float64 value, while
    // valInt stores values that are exact integers. Both have to go first
    // in the struct to guarantee alignment for atomic operations.
    // http://golang.org/pkg/sync/atomic/#pkg-note-BUG
    valBits uint64
    valInt  uint64

    selfCollector
    desc *Desc

    labelPairs []*dto.LabelPair
}

They used unsigned int64 type for valInt counter. So once it exceeds the limit of int64, it will be set to zero again. I guess it will be similar for other client libraries too.