postgres_exporter/pkg/queries/metricmaps/decoding.go

package metricmaps

// Turn the MetricMap column mapping into a prometheus descriptor mapping.
func makeDescMap(pgVersion semver.Version, serverLabels prometheus.Labels, metricMaps map[string]intermediateMetricMap) map[string]MetricMapNamespace {
	var metricMap = make(map[string]MetricMapNamespace)

	for namespace, intermediateMappings := range metricMaps {
		thisMap := make(map[string]MetricMap)

		// Get the constant labels
		var variableLabels []string
		for columnName, columnMapping := range intermediateMappings.columnMappings {
			if columnMapping.usage == queries.LABEL {
				variableLabels = append(variableLabels, columnName)
			}
		}

		for columnName, columnMapping := range intermediateMappings.columnMappings {
			// Check column version compatibility for the current map
			// Force to discard if not compatible.
			if columnMapping.supportedVersions != nil {
				if !columnMapping.supportedVersions(pgVersion) {
					// It's very useful to be able to see what columns are being
					// rejected.
					log.Debugln(columnName, "is being forced to discard due to version incompatibility.")
					thisMap[columnName] = MetricMap{
						discard: true,
						conversion: func(_ interface{}) (float64, bool) {
							return math.NaN(), true
						},
					}
					continue
				}
			}

			// Determine how to convert the column based on its usage.
			// nolint: dupl
			switch columnMapping.usage {
			case queries.DISCARD, queries.LABEL:
				thisMap[columnName] = MetricMap{
					discard: true,
					conversion: func(_ interface{}) (float64, bool) {
						return math.NaN(), true
					},
				}
			case queries.COUNTER:
				thisMap[columnName] = MetricMap{
					vtype: prometheus.CounterValue,
					desc:  prometheus.NewDesc(fmt.Sprintf("%s_%s", namespace, columnName), columnMapping.description, variableLabels, serverLabels),
					conversion: func(in interface{}) (float64, bool) {
						return pgdbconv.DBToFloat64(in)
					},
				}
			case queries.GAUGE:
				thisMap[columnName] = MetricMap{
					vtype: prometheus.GaugeValue,
					desc:  prometheus.NewDesc(fmt.Sprintf("%s_%s", namespace, columnName), columnMapping.description, variableLabels, serverLabels),
					conversion: func(in interface{}) (float64, bool) {
						return pgdbconv.DBToFloat64(in)
					},
				}
			case queries.MAPPEDMETRIC:
				thisMap[columnName] = MetricMap{
					vtype: prometheus.GaugeValue,
					desc:  prometheus.NewDesc(fmt.Sprintf("%s_%s", namespace, columnName), columnMapping.description, variableLabels, serverLabels),
					conversion: func(in interface{}) (float64, bool) {
						text, ok := in.(string)
						if !ok {
							return math.NaN(), false
						}

						val, ok := columnMapping.mapping[text]
						if !ok {
							return math.NaN(), false
						}
						return val, true
					},
				}
			case queries.DURATION:
				thisMap[columnName] = MetricMap{
					vtype: prometheus.GaugeValue,
					desc:  prometheus.NewDesc(fmt.Sprintf("%s_%s_milliseconds", namespace, columnName), columnMapping.description, variableLabels, serverLabels),
					conversion: func(in interface{}) (float64, bool) {
						var durationString string
						switch t := in.(type) {
						case []byte:
							durationString = string(t)
						case string:
							durationString = t
						default:
							log.Errorln("DURATION conversion metric was not a string")
							return math.NaN(), false
						}

						if durationString == "-1" {
							return math.NaN(), false
						}

						d, err := time.ParseDuration(durationString)
						if err != nil {
							log.Errorln("Failed converting result to metric:", columnName, in, err)
							return math.NaN(), false
						}
						return float64(d / time.Millisecond), true
					},
				}
			}
		}

		metricMap[namespace] = MetricMapNamespace{
			labels:         variableLabels,
			columnMappings: thisMap,
			master:         intermediateMappings.master,
			cacheSeconds:   intermediateMappings.cacheSeconds}
	}

	return metricMap
}