app/vminsert: prevent from adding and/or selecting labels with empty values

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/600

app/vminsert/influx/request_handler.go

@@ -11,7 +11,6 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vminsert/relabel"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/auth"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
-	"github.com/VictoriaMetrics/VictoriaMetrics/lib/prompb"
 	parser "github.com/VictoriaMetrics/VictoriaMetrics/lib/protoparser/influx"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/tenantmetrics"
@@ -95,9 +94,9 @@ func insertRows(at *auth.Token, db string, rows []parser.Row, mayOverrideAccount
 			ctx.metricGroupBuf = append(ctx.metricGroupBuf, *measurementFieldSeparator...)
 		}
 		metricGroupPrefixLen := len(ctx.metricGroupBuf)
-		var labels []prompb.Label
-		if !hasRelabeling {
-			labels = ic.Labels
+		labels := ic.Labels
+		if hasRelabeling {
+			labels = nil
 		}
 		ic.MetricNameBuf = storage.MarshalMetricNameRaw(ic.MetricNameBuf[:0], atCopy.AccountID, atCopy.ProjectID, labels)
 		metricNameBufLen := len(ic.MetricNameBuf)
@@ -110,15 +109,14 @@ func insertRows(at *auth.Token, db string, rows []parser.Row, mayOverrideAccount
 			metricGroup := bytesutil.ToUnsafeString(ctx.metricGroupBuf)
 			ic.Labels = ic.Labels[:labelsLen]
 			ic.AddLabel("", metricGroup)
-			if hasRelabeling {
-				ic.ApplyRelabeling()
-				labels = ic.Labels
-				if len(labels) == 0 {
-					// Skip metric without labels.
-					continue
-				}
-			} else {
-				labels = ic.Labels[labelsLen : labelsLen+1]
+			ic.ApplyRelabeling() // this must be called even if !hasRelabeling in order to remove labels with empty values
+			if len(ic.Labels) == 0 {
+				// Skip metric without labels.
+				continue
+			}
+			labels = ic.Labels
+			if !hasRelabeling {
+				labels = labels[labelsLen : labelsLen+1]
 			}
 			ic.MetricNameBuf = ic.MetricNameBuf[:metricNameBufLen]
 			for i := range labels {

app/vminsert/relabel/relabel.go

@@ -81,8 +81,29 @@ func (ctx *Ctx) Reset() {
 //
 // The returned labels are valid until the next call to ApplyRelabeling.
 func (ctx *Ctx) ApplyRelabeling(labels []prompb.Label) []prompb.Label {
+	// Remove labels with empty values, since such labels have no sense.
+	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/600 .
+	hasEmptyValues := false
+	for _, label := range labels {
+		if len(label.Value) == 0 {
+			hasEmptyValues = true
+			break
+		}
+	}
+	if hasEmptyValues {
+		dst := labels[:0]
+		for _, label := range labels {
+			if len(label.Value) == 0 {
+				continue
+			}
+			dst = append(dst, label)
+		}
+		labels = dst
+	}
+
 	prcs := prcsGlobal.Load().(*[]promrelabel.ParsedRelabelConfig)
 	if len(*prcs) == 0 {
+		// There are no relabeling rules.
 		return labels
 	}
 	// Convert src to prompbmarshal.Label format suitable for relabeling.

lib/storage/index_db.go

@@ -761,6 +761,7 @@ func (db *indexDB) SearchTagKeys(accountID, projectID uint32, maxTagKeys int) ([
 
 	keys := make([]string, 0, len(tks))
 	for key := range tks {
+		// Do not skip empty keys, since they are converted to __name__
 		keys = append(keys, key)
 	}
 
@@ -828,6 +829,11 @@ func (db *indexDB) SearchTagValues(accountID, projectID uint32, tagKey []byte, m
 
 	tagValues := make([]string, 0, len(tvs))
 	for tv := range tvs {
+		if len(tv) == 0 {
+			// Skip empty values, since they have no any meaning.
+			// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/600
+			continue
+		}
 		tagValues = append(tagValues, tv)
 	}