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metric.go
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metric.go
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package sql_exporter
import (
"fmt"
"sort"
"github.com/free/sql_exporter/config"
"github.com/free/sql_exporter/errors"
"github.com/golang/protobuf/proto"
"github.com/prometheus/client_golang/prometheus"
dto "github.com/prometheus/client_model/go"
)
// MetricDesc is a descriptor for a family of metrics, sharing the same name, help, labes, type.
type MetricDesc interface {
Name() string
Help() string
ValueType() prometheus.ValueType
ConstLabels() []*dto.LabelPair
Labels() []string
LogContext() string
}
//
// MetricFamily
//
// MetricFamily implements MetricDesc for SQL metrics, with logic for populating its labels and values from sql.Rows.
type MetricFamily struct {
config *config.MetricConfig
constLabels []*dto.LabelPair
labels []string
logContext string
}
// NewMetricFamily creates a new MetricFamily with the given metric config and const labels (e.g. job and instance).
func NewMetricFamily(logContext string, mc *config.MetricConfig, constLabels []*dto.LabelPair) (*MetricFamily, errors.WithContext) {
logContext = fmt.Sprintf("%s, metric=%q", logContext, mc.Name)
if len(mc.Values) == 0 {
return nil, errors.New(logContext, "no value column defined")
}
if len(mc.Values) > 1 && mc.ValueLabel == "" {
return nil, errors.New(logContext, "multiple values but no value label")
}
labels := make([]string, 0, len(mc.KeyLabels)+1)
labels = append(labels, mc.KeyLabels...)
if mc.ValueLabel != "" {
labels = append(labels, mc.ValueLabel)
}
// Create a copy of original slice to avoid modifying constLabels
sortedLabels := append(constLabels[:0:0], constLabels...)
for k, v := range mc.StaticLabels {
sortedLabels = append(sortedLabels, &dto.LabelPair{
Name: proto.String(k),
Value: proto.String(v),
})
}
sort.Sort(labelPairSorter(sortedLabels))
return &MetricFamily{
config: mc,
constLabels: sortedLabels,
labels: labels,
logContext: logContext,
}, nil
}
// Collect is the equivalent of prometheus.Collector.Collect() but takes a Query output map to populate values from.
func (mf MetricFamily) Collect(row map[string]interface{}, ch chan<- Metric) {
labelValues := make([]string, len(mf.labels))
for i, label := range mf.config.KeyLabels {
labelValues[i] = row[label].(string)
}
for _, v := range mf.config.Values {
if mf.config.ValueLabel != "" {
labelValues[len(labelValues)-1] = v
}
value := row[v].(float64)
ch <- NewMetric(&mf, value, labelValues...)
}
}
// Name implements MetricDesc.
func (mf MetricFamily) Name() string {
return mf.config.Name
}
// Help implements MetricDesc.
func (mf MetricFamily) Help() string {
return mf.config.Help
}
// ValueType implements MetricDesc.
func (mf MetricFamily) ValueType() prometheus.ValueType {
return mf.config.ValueType()
}
// ConstLabels implements MetricDesc.
func (mf MetricFamily) ConstLabels() []*dto.LabelPair {
return mf.constLabels
}
// Labels implements MetricDesc.
func (mf MetricFamily) Labels() []string {
return mf.labels
}
// LogContext implements MetricDesc.
func (mf MetricFamily) LogContext() string {
return mf.logContext
}
//
// automaticMetricDesc
//
// automaticMetric is a MetricDesc for automatically generated metrics (e.g. `up` and `scrape_duration`).
type automaticMetricDesc struct {
name string
help string
valueType prometheus.ValueType
labels []string
constLabels []*dto.LabelPair
logContext string
}
// NewAutomaticMetricDesc creates a MetricDesc for automatically generated metrics.
func NewAutomaticMetricDesc(
logContext, name, help string, valueType prometheus.ValueType, constLabels []*dto.LabelPair, labels ...string) MetricDesc {
return &automaticMetricDesc{
name: name,
help: help,
valueType: valueType,
constLabels: constLabels,
labels: labels,
logContext: logContext,
}
}
// Name implements MetricDesc.
func (a automaticMetricDesc) Name() string {
return a.name
}
// Help implements MetricDesc.
func (a automaticMetricDesc) Help() string {
return a.help
}
// ValueType implements MetricDesc.
func (a automaticMetricDesc) ValueType() prometheus.ValueType {
return a.valueType
}
// ConstLabels implements MetricDesc.
func (a automaticMetricDesc) ConstLabels() []*dto.LabelPair {
return a.constLabels
}
// Labels implements MetricDesc.
func (a automaticMetricDesc) Labels() []string {
return a.labels
}
// LogContext implements MetricDesc.
func (a automaticMetricDesc) LogContext() string {
return a.logContext
}
//
// Metric
//
// A Metric models a single sample value with its meta data being exported to Prometheus.
type Metric interface {
Desc() MetricDesc
Write(out *dto.Metric) errors.WithContext
}
// NewMetric returns a metric with one fixed value that cannot be changed.
//
// NewMetric panics if the length of labelValues is not consistent with desc.labels().
func NewMetric(desc MetricDesc, value float64, labelValues ...string) Metric {
if len(desc.Labels()) != len(labelValues) {
panic(fmt.Sprintf("[%s] expected %d labels, got %d", desc.LogContext(), len(desc.Labels()), len(labelValues)))
}
return &constMetric{
desc: desc,
val: value,
labelPairs: makeLabelPairs(desc, labelValues),
}
}
// constMetric is a metric with one fixed value that cannot be changed.
type constMetric struct {
desc MetricDesc
val float64
labelPairs []*dto.LabelPair
}
// Desc implements Metric.
func (m *constMetric) Desc() MetricDesc {
return m.desc
}
// Write implements Metric.
func (m *constMetric) Write(out *dto.Metric) errors.WithContext {
out.Label = m.labelPairs
switch t := m.desc.ValueType(); t {
case prometheus.CounterValue:
out.Counter = &dto.Counter{Value: proto.Float64(m.val)}
case prometheus.GaugeValue:
out.Gauge = &dto.Gauge{Value: proto.Float64(m.val)}
default:
return errors.Errorf(m.desc.LogContext(), "encountered unknown type %v", t)
}
return nil
}
func makeLabelPairs(desc MetricDesc, labelValues []string) []*dto.LabelPair {
labels := desc.Labels()
constLabels := desc.ConstLabels()
totalLen := len(labels) + len(constLabels)
if totalLen == 0 {
// Super fast path.
return nil
}
if len(labels) == 0 {
// Moderately fast path.
return constLabels
}
labelPairs := make([]*dto.LabelPair, 0, totalLen)
for i, label := range labels {
labelPairs = append(labelPairs, &dto.LabelPair{
Name: proto.String(label),
Value: proto.String(labelValues[i]),
})
}
labelPairs = append(labelPairs, constLabels...)
sort.Sort(labelPairSorter(labelPairs))
return labelPairs
}
// labelPairSorter implements sort.Interface.
// It provides a sortable version of a slice of dto.LabelPair pointers.
type labelPairSorter []*dto.LabelPair
func (s labelPairSorter) Len() int {
return len(s)
}
func (s labelPairSorter) Swap(i, j int) {
s[i], s[j] = s[j], s[i]
}
func (s labelPairSorter) Less(i, j int) bool {
return s[i].GetName() < s[j].GetName()
}
type invalidMetric struct {
err errors.WithContext
}
// NewInvalidMetric returns a metric whose Write method always returns the provided error.
func NewInvalidMetric(err errors.WithContext) Metric {
return invalidMetric{err}
}
func (m invalidMetric) Desc() MetricDesc { return nil }
func (m invalidMetric) Write(*dto.Metric) errors.WithContext { return m.err }