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# A buffered Prometheus reporter
See `examples/prometheus_main.go` for an end to end example.
## Options
You can use a specific Prometheus registry, and you can use
either summaries or histograms for timers.
The reporter options are:
```go
// Options is a set of options for the tally reporter.
type Options struct {
// Registerer is the prometheus registerer to register
// metrics with. Use nil to specify the default registerer.
Registerer prom.Registerer
// DefaultTimerType is the default type timer type to create
// when using timers. It's default value is a histogram timer type.
DefaultTimerType TimerType
// DefaultHistogramBuckets is the default histogram buckets
// to use. Use nil to specify the default histogram buckets.
DefaultHistogramBuckets []float64
// DefaultSummaryObjectives is the default summary objectives
// to use. Use nil to specify the default summary objectives.
DefaultSummaryObjectives map[float64]float64
// OnRegisterError defines a method to call to when registering
// a metric with the registerer fails. Use nil to specify
// to panic by default when registering a metric fails.
OnRegisterError func(err error)
}
```
The timer types are:
```go
// TimerType describes a type of timer
type TimerType int
const (
// SummaryTimerType is a timer type that reports into a summary
SummaryTimerType TimerType = iota
// HistogramTimerType is a timer type that reports into a histogram
HistogramTimerType
)
```
You can also pre-register help description text ahead of using a metric
that will be named and tagged identically with `tally`. You can also
access the Prometheus HTTP handler directly.
The returned reporter interface:
```go
// Reporter is a Prometheus backed tally reporter.
type Reporter interface {
tally.CachedStatsReporter
// HTTPHandler provides the Prometheus HTTP scrape handler.
HTTPHandler() http.Handler
// RegisterCounter is a helper method to initialize a counter
// in the Prometheus backend with a given help text.
// If not called explicitly, the Reporter will create one for
// you on first use, with a not super helpful HELP string.
RegisterCounter(
name string,
tagKeys []string,
desc string,
) (*prom.CounterVec, error)
// RegisterGauge is a helper method to initialize a gauge
// in the prometheus backend with a given help text.
// If not called explicitly, the Reporter will create one for
// you on first use, with a not super helpful HELP string.
RegisterGauge(
name string,
tagKeys []string,
desc string,
) (*prom.GaugeVec, error)
// RegisterTimer is a helper method to initialize a timer
// summary or histogram vector in the prometheus backend
// with a given help text.
// If not called explicitly, the Reporter will create one for
// you on first use, with a not super helpful HELP string.
// You may pass opts as nil to get the default timer type
// and objectives/buckets.
// You may also pass objectives/buckets as nil in opts to
// get the default objectives/buckets for the specified
// timer type.
RegisterTimer(
name string,
tagKeys []string,
desc string,
opts *RegisterTimerOptions,
) (TimerUnion, error)
}
```
The register timer options:
```go
// RegisterTimerOptions provides options when registering a timer on demand.
// By default you can pass nil for the options to get the reporter defaults.
type RegisterTimerOptions struct {
TimerType TimerType
HistogramBuckets []float64
SummaryObjectives map[float64]float64
}
```
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