add histogram support

Author: idoqo

exporter/metrics.go

@@ -16,6 +16,7 @@
 package exporter
 
 import (
+	"math"
 	"regexp"
 	"strings"
 	"sync"
@@ -370,9 +371,119 @@ func makeMetrics(prefix string, m bson.M, labels map[string]string, compatibleMo
 	return res
 }
 
+// isHistogramArray detects histogram arrays in the MongoDB structures.
+// Currently, we assume histograms are in the form:
+//
+//	"histograms": {
+//	  "classicMicros": [
+//	       {
+//	            "lowerBound": {
+//	                 "low": 0,
+//	                 "high": 0,
+//	                 "unsigned": false
+//	            },
+//	            "count": {
+//	                 "low": 0,
+//	                 "high": 0,
+//	                 "unsigned": false
+//	            }
+//	       },
+//	       ...
+//	  ]
+//	}
+//
+// The "histograms" key is the one that tells us this is a histogram array.
+// Each element in the array must have a "lowerBound" and a "count" field.
+func isHistogramArray(prefix string, slice primitive.A) bool {
+	if !strings.Contains(prefix, "histograms") || len(slice) == 0 {
+		return false
+	}
+
+	if bucket, ok := slice[0].(bson.M); ok {
+		_, hasLowerBound := bucket["lowerBound"]
+		_, hasCount := bucket["count"]
+		return hasLowerBound && hasCount
+	}
+
+	return false
+}
+
+func processHistogramArray(prefix string, histogramArray primitive.A, labels map[string]string) []prometheus.Metric {
+	var metrics []prometheus.Metric
+	histogramName := strings.TrimSuffix(prefix, ".histograms")
+
+	buckets := make(map[float64]uint64)
+	var totalCount uint64
+
+	for _, item := range histogramArray {
+		bucket, ok := item.(bson.M)
+		if !ok {
+			continue
+		}
+
+		lowerBoundVal, hasBound := bucket["lowerBound"]
+		countVal, hasCount := bucket["count"]
+
+		if !hasBound || !hasCount {
+			continue
+		}
+
+		bound, err := asFloat64(lowerBoundVal)
+		if err != nil || bound == nil {
+			continue
+		}
+
+		count, err := asFloat64(countVal)
+		if err != nil || count == nil {
+			continue
+		}
+
+		buckets[*bound] += uint64(*count)
+		totalCount += uint64(*count)
+	}
+
+	// Add +Inf bucket
+	if buckets[math.Inf(1)] == 0 {
+		buckets[math.Inf(1)] = totalCount
+	}
+
+	if len(buckets) > 0 {
+		labelNames := make([]string, 0, len(labels))
+		labelValues := make([]string, 0, len(labels))
+		for k, v := range labels {
+			labelNames = append(labelNames, k)
+			labelValues = append(labelValues, v)
+		}
+
+		desc := prometheus.NewDesc(
+			prometheusize(histogramName),
+			metricHelp("", histogramName),
+			labelNames,
+			nil,
+		)
+
+		histogram, err := prometheus.NewConstHistogram(
+			desc,
+			totalCount,
+			0, // sum - we don't have this from MongoDB data
+			buckets,
+			labelValues...,
+		)
+
+		if err == nil {
+			metrics = append(metrics, histogram)
+		}
+	}
+
+	return metrics
+}
+
 // Extract maps from arrays. Only some structures like replicasets have arrays of members
 // and each member is represented by a map[string]interface{}.
 func processSlice(prefix string, v []interface{}, commonLabels map[string]string, compatibleMode bool) []prometheus.Metric {
+	if isHistogramArray(prefix, v) {
+		return processHistogramArray(prefix, v, commonLabels)
+	}
 	metrics := make([]prometheus.Metric, 0)
 	labels := make(map[string]string)
 	for name, value := range commonLabels {

exporter/v1_compatibility.go

@@ -341,11 +341,6 @@ var conversions = []conversion{
 			"writeConflicts": "writeConflicts",
 		},
 	},
-	{
-		oldName:     "mongodb_mongod_metrics_query_executor_total",
-		prefix:      "mongodb_ss_metrics_query",
-		suffixLabel: "state",
-	},
 	{
 		oldName: "mongodb_mongod_metrics_record_moves_total",
 		newName: "mongodb_ss_metrics_record_moves",