[feature] Add a Descending index metric name override flag (#435)

Fields with descending order in a MongoDB index have '-1' in index name.
'-' is not a valid character in data model for Prometheus. Hence it will be
replaced with 'DESC' to remove ambiguity between indexes with use of
new flag in exporter.

Co-authored-by: Denys Kondratenko <[email protected]>
Co-authored-by: Shashank Sinha <[email protected]>

Author: 3 people

README.md

@@ -42,6 +42,7 @@ the current version.
 |\-\-no-collector.replicasetstatus|Disable collecting metrics from replSetGetStatus||
 |\-\-collector.dbstats|Enable collecting metrics from dbStats||
 |\-\-enable.top|Enable collecting metrics from top admin command||
+|\-\-metrics.overridedescendingindex| Enable descending index name override to replace -1 with _DESC ||
 |--version|Show version and exit|
 
 ### Build the exporter

exporter/exporter.go

@@ -65,6 +65,8 @@ type Opts struct {
 	EnableIndexStats       bool
 	EnableCollStats        bool
 
+	EnableOverrideDescendingIndex bool
+
 	IndexStatsCollections []string
 	Logger                *logrus.Logger
 	Path                  string
@@ -165,7 +167,8 @@ func (e *Exporter) makeRegistry(ctx context.Context, client *mongo.Client, topol
 	// If we manually set the collection names we want or auto discovery is set.
 	if (len(e.opts.IndexStatsCollections) > 0 || e.opts.DiscoveringMode) && e.opts.EnableIndexStats && limitsOk && requestOpts.EnableIndexStats {
 		ic := newIndexStatsCollector(ctx, client, e.opts.Logger,
-			e.opts.DiscoveringMode, topologyInfo, e.opts.IndexStatsCollections)
+			e.opts.DiscoveringMode, e.opts.EnableOverrideDescendingIndex,
+			topologyInfo, e.opts.IndexStatsCollections)
 		registry.MustRegister(ic)
 	}
 

exporter/indexstats_collector.go

@@ -31,21 +31,24 @@ type indexstatsCollector struct {
 	ctx  context.Context
 	base *baseCollector
 
-	discoveringMode bool
-	topologyInfo    labelsGetter
+	discoveringMode         bool
+	overrideDescendingIndex bool
+	topologyInfo            labelsGetter
 
 	collections []string
 }
 
 // newIndexStatsCollector creates a collector for statistics on index usage.
-func newIndexStatsCollector(ctx context.Context, client *mongo.Client, logger *logrus.Logger, discovery bool, topology labelsGetter, collections []string) *indexstatsCollector {
+func newIndexStatsCollector(ctx context.Context, client *mongo.Client, logger *logrus.Logger, discovery, overrideDescendingIndex bool, topology labelsGetter, collections []string) *indexstatsCollector {
 	return &indexstatsCollector{
 		ctx:  ctx,
 		base: newBaseCollector(client, logger),
 
-		discoveringMode: discovery,
-		topologyInfo:    topology,
-		collections:     collections,
+		discoveringMode:         discovery,
+		topologyInfo:            topology,
+		overrideDescendingIndex: overrideDescendingIndex,
+
+		collections: collections,
 	}
 }
 
@@ -106,13 +109,19 @@ func (d *indexstatsCollector) collect(ch chan<- prometheus.Metric) {
 		debugResult(d.base.logger, stats)
 
 		for _, metric := range stats {
+			indexName := fmt.Sprintf("%s", metric["name"])
+			// Override the label name
+			if d.overrideDescendingIndex {
+				indexName = strings.ReplaceAll(fmt.Sprintf("%s", metric["name"]), "-1", "DESC")
+			}
+
 			// prefix and labels are needed to avoid duplicated metric names since the metrics are the
 			// same, for different collections.
 			prefix := "indexstats"
 			labels := d.topologyInfo.baseLabels()
 			labels["database"] = database
 			labels["collection"] = collection
-			labels["key_name"] = fmt.Sprintf("%s", metric["name"])
+			labels["key_name"] = indexName
 
 			metrics := sanitizeMetrics(metric)
 			for _, metric := range makeMetrics(prefix, metrics, labels, false) {

exporter/indexstats_collector_test.go

@@ -65,7 +65,7 @@ func TestIndexStatsCollector(t *testing.T) {
 	}
 
 	collection := []string{"testdb.testcol_00", "testdb.testcol_01", "testdb.testcol_02"}
-	c := newIndexStatsCollector(ctx, client, logrus.New(), false, ti, collection)
+	c := newIndexStatsCollector(ctx, client, logrus.New(), false, true, ti, collection)
 
 	// The last \n at the end of this string is important
 	expected := strings.NewReader(`
@@ -83,6 +83,54 @@ mongodb_indexstats_accesses_ops{collection="testcol_02",database="testdb",key_na
 	assert.NoError(t, err)
 }
 
+func TestDescendingIndexOverride(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
+	defer cancel()
+
+	client := tu.DefaultTestClient(ctx, t)
+
+	ti := labelsGetterMock{}
+
+	database := client.Database("testdb")
+	database.Drop(ctx)       //nolint:errcheck
+	defer database.Drop(ctx) //nolint:errcheck
+
+	for i := 0; i < 3; i++ {
+		collection := fmt.Sprintf("testcol_%02d", i)
+		for j := 0; j < 10; j++ {
+			_, err := database.Collection(collection).InsertOne(ctx, bson.M{"f1": j, "f2": "2"})
+			assert.NoError(t, err)
+		}
+
+		descendingMod := mongo.IndexModel{Keys: bson.M{"f1": -1}}
+		_, err := database.Collection(collection).Indexes().CreateOne(ctx, descendingMod)
+		assert.NoError(t, err)
+
+		ascendingMod := mongo.IndexModel{Keys: bson.M{"f1": 1}}
+		_, err = database.Collection(collection).Indexes().CreateOne(ctx, ascendingMod)
+		assert.NoError(t, err)
+	}
+
+	collection := []string{"testdb.testcol_00", "testdb.testcol_01", "testdb.testcol_02"}
+	c := newIndexStatsCollector(ctx, client, logrus.New(), false, true, ti, collection)
+
+	// The last \n at the end of this string is important
+	expected := strings.NewReader(`
+  # HELP mongodb_indexstats_accesses_ops indexstats.accesses.
+  # TYPE mongodb_indexstats_accesses_ops untyped
+  mongodb_indexstats_accesses_ops{collection="testcol_00",database="testdb",key_name="_id_"} 0
+  mongodb_indexstats_accesses_ops{collection="testcol_00",database="testdb",key_name="f1_1"} 0
+  mongodb_indexstats_accesses_ops{collection="testcol_00",database="testdb",key_name="f1_DESC"} 0
+  mongodb_indexstats_accesses_ops{collection="testcol_01",database="testdb",key_name="_id_"} 0
+  mongodb_indexstats_accesses_ops{collection="testcol_01",database="testdb",key_name="f1_1"} 0
+  mongodb_indexstats_accesses_ops{collection="testcol_01",database="testdb",key_name="f1_DESC"} 0
+  mongodb_indexstats_accesses_ops{collection="testcol_02",database="testdb",key_name="_id_"} 0
+  mongodb_indexstats_accesses_ops{collection="testcol_02",database="testdb",key_name="f1_1"} 0
+  mongodb_indexstats_accesses_ops{collection="testcol_02",database="testdb",key_name="f1_DESC"} 0` + "\n")
+	err := testutil.CollectAndCompare(c, expected)
+	assert.NoError(t, err)
+}
+
 func TestSanitize(t *testing.T) {
 	t.Run("With building", func(t *testing.T) {
 		in := bson.M{

main.go

@@ -51,6 +51,8 @@ type GlobalFlags struct {
 	EnableIndexStats       bool `name:"collector.indexstats" help:"Enable collecting metrics from $indexStats"`
 	EnableCollStats        bool `name:"collector.collstats" help:"Enable collecting metrics from $collStats"`
 
+	EnableOverrideDescendingIndex bool `name:"metrics.overridedescendingindex" help:"Enable descending index name override to replace -1 with _DESC"`
+
 	CollectAll bool `name:"collect-all" help:"Enable all collectors. Same as specifying all --collector.<name>"`
 
 	CollStatsLimit int `name:"collector.collstats-limit" help:"Disable collstats, dbstats, topmetrics and indexstats collector if there are more than <n> collections. 0=No limit" default:"0"`
@@ -126,6 +128,8 @@ func buildExporter(opts GlobalFlags) *exporter.Exporter {
 		EnableIndexStats:       opts.EnableIndexStats,
 		EnableCollStats:        opts.EnableCollStats,
 
+		EnableOverrideDescendingIndex: opts.EnableOverrideDescendingIndex,
+
 		CollStatsLimit: opts.CollStatsLimit,
 		CollectAll:     opts.CollectAll,
 	}