lib/storage: use binary search instead of full scan for skipping artificial tags when searching for tag names or tag values

This should improve performance for /api/v1/labels and /api/v1/label/<label_name>/values

See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2200

docs/CHANGELOG.md

@@ -15,6 +15,7 @@ The following tip changes can be tested by building VictoriaMetrics components f
 ## tip
 
 
+* BUGFIX: fix a bug, which could significantly slow down requests to `/api/v1/labels` and `/api/v1/label/<label_name>/values`. These APIs are used by Grafana for auto-completion of label names and label values. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2200).
 * BUGFIX: vmalert: add support for `$externalLabels` and `$externalURL` template vars in the same way as Prometheus does. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2193).
 * BUGFIX: update default value for `-promscrape.fileSDCheckInterval`, so it matches default duration used by Prometheus for checking for updates in `file_sd_configs`. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2187). Thanks to @corporate-gadfly for the fix.
 

lib/storage/index_db.go

@@ -801,12 +801,9 @@ func (is *indexSearch) searchTagKeysOnDate(tks map[string]struct{}, date uint64,
 			continue
 		}
 		key := mp.Tag.Key
-		if isArtificialTagKey(key) {
+		if !isArtificialTagKey(key) {
-			// Skip artificially created tag key.
-			continue
-		}
-		// Store tag key.
 			tks[string(key)] = struct{}{}
+		}
 
 		// Search for the next tag key.
 		// The last char in kb.B must be tagSeparatorChar.
@@ -880,12 +877,9 @@ func (is *indexSearch) searchTagKeys(tks map[string]struct{}, maxTagKeys int) er
 			continue
 		}
 		key := mp.Tag.Key
-		if isArtificialTagKey(key) {
+		if !isArtificialTagKey(key) {
-			// Skip artificailly created tag keys.
-			continue
-		}
-		// Store tag key.
 			tks[string(key)] = struct{}{}
+		}
 
 		// Search for the next tag key.
 		// The last char in kb.B must be tagSeparatorChar.
@@ -1000,22 +994,25 @@ func (is *indexSearch) searchTagValuesOnDate(tvs map[string]struct{}, tagKey []b
 			continue
 		}
 
-		// Store tag value
+		skipTag := isArtificialTagKey(mp.Tag.Key)
+		if !skipTag {
 			tvs[string(mp.Tag.Value)] = struct{}{}
-
 			if mp.MetricIDsLen() < maxMetricIDsPerRow/2 {
 				// There is no need in searching for the next tag value,
 				// since it is likely it is located in the next row,
 				// because the current row contains incomplete metricIDs set.
 				continue
 			}
+		}
 		// Search for the next tag value.
 		// The last char in kb.B must be tagSeparatorChar.
 		// Just increment it in order to jump to the next tag value.
 		kb.B = is.marshalCommonPrefix(kb.B[:0], nsPrefixDateTagToMetricIDs)
 		kb.B = encoding.MarshalUint64(kb.B, date)
 		kb.B = marshalTagValue(kb.B, mp.Tag.Key)
+		if !skipTag {
 			kb.B = marshalTagValue(kb.B, mp.Tag.Value)
+		}
 		kb.B[len(kb.B)-1]++
 		ts.Seek(kb.B)
 	}
@@ -1085,21 +1082,24 @@ func (is *indexSearch) searchTagValues(tvs map[string]struct{}, tagKey []byte, m
 			continue
 		}
 
-		// Store tag value
+		skipTag := isArtificialTagKey(mp.Tag.Key)
+		if !skipTag {
 			tvs[string(mp.Tag.Value)] = struct{}{}
-
 			if mp.MetricIDsLen() < maxMetricIDsPerRow/2 {
 				// There is no need in searching for the next tag value,
 				// since it is likely it is located in the next row,
 				// because the current row contains incomplete metricIDs set.
 				continue
 			}
+		}
 		// Search for the next tag value.
 		// The last char in kb.B must be tagSeparatorChar.
 		// Just increment it in order to jump to the next tag value.
 		kb.B = is.marshalCommonPrefix(kb.B[:0], nsPrefixTagToMetricIDs)
 		kb.B = marshalTagValue(kb.B, mp.Tag.Key)
+		if !skipTag {
 			kb.B = marshalTagValue(kb.B, mp.Tag.Value)
+		}
 		kb.B[len(kb.B)-1]++
 		ts.Seek(kb.B)
 	}