Loki: Default to /labels API with query param instead of /series API (#97935)

* feat(loki-labels-api): add feature toggle

* feat(loki-labels-api): default to `/labels` API

docs/sources/setup-grafana/configure-grafana/feature-toggles/index.md

@@ -84,6 +84,7 @@ Most [generally available](https://grafana.com/docs/release-life-cycle/#general-
 | `zipkinBackendMigration`               | Enables querying Zipkin data source without the proxy                                                                                                              | Yes                |
 | `alertingUIOptimizeReducer`            | Enables removing the reducer from the alerting UI when creating a new alert rule and using instant query                                                           | Yes                |
 | `azureMonitorEnableUserAuth`           | Enables user auth for Azure Monitor datasource only                                                                                                                | Yes                |
+| `lokiLabelNamesQueryApi`               | Defaults to using the Loki `/labels` API instead of `/series`                                                                                                      | Yes                |
 
 ## Public preview feature toggles
 

packages/grafana-data/src/types/featureToggles.gen.ts

@@ -244,4 +244,5 @@ export interface FeatureToggles {
   feedbackButton?: boolean;
   elasticsearchCrossClusterSearch?: boolean;
   unifiedHistory?: boolean;
+  lokiLabelNamesQueryApi?: boolean;
 }

pkg/services/featuremgmt/registry.go

@@ -1689,6 +1689,13 @@ var (
 			Owner:        grafanaFrontendPlatformSquad,
 			FrontendOnly: true,
 		},
+		{
+			Name:        "lokiLabelNamesQueryApi",
+			Description: "Defaults to using the Loki `/labels` API instead of `/series`",
+			Stage:       FeatureStageGeneralAvailability,
+			Owner:       grafanaObservabilityLogsSquad,
+			Expression:  "true",
+		},
 	}
 )
 

pkg/services/featuremgmt/toggles_gen.csv

@@ -225,3 +225,4 @@ alertingNotificationsStepMode,experimental,@grafana/alerting-squad,false,false,t
 feedbackButton,experimental,@grafana/grafana-operator-experience-squad,false,false,false
 elasticsearchCrossClusterSearch,preview,@grafana/aws-datasources,false,false,false
 unifiedHistory,experimental,@grafana/grafana-frontend-platform,false,false,true
+lokiLabelNamesQueryApi,GA,@grafana/observability-logs,false,false,false

pkg/services/featuremgmt/toggles_gen.go

@@ -910,4 +910,8 @@ const (
 	// FlagUnifiedHistory
 	// Displays the navigation history so the user can navigate back to previous pages
 	FlagUnifiedHistory = "unifiedHistory"
+
+	// FlagLokiLabelNamesQueryApi
+	// Defaults to using the Loki `/labels` API instead of `/series`
+	FlagLokiLabelNamesQueryApi = "lokiLabelNamesQueryApi"
 )

pkg/services/featuremgmt/toggles_gen.json

@@ -2095,6 +2095,19 @@
         "codeowner": "@grafana/observability-logs"
       }
     },
+    {
+      "metadata": {
+        "name": "lokiLabelNamesQueryApi",
+        "resourceVersion": "1734096677730",
+        "creationTimestamp": "2024-12-13T13:31:17Z"
+      },
+      "spec": {
+        "description": "Defaults to using the Loki `/labels` API instead of `/series`",
+        "stage": "GA",
+        "codeowner": "@grafana/observability-logs",
+        "expression": "true"
+      }
+    },
     {
       "metadata": {
         "name": "lokiLogsDataplane",

public/app/plugins/datasource/loki/LanguageProvider.test.ts

@@ -428,17 +428,51 @@ describe('Language completion provider', () => {
       expect(instance.request).toHaveBeenCalledWith('labels', datasourceWithLabels.getTimeRangeParams(mockTimeRange));
     });
 
-    it('should use series endpoint for request with stream selector', async () => {
-      const datasourceWithLabels = setup({});
-      datasourceWithLabels.languageProvider.request = jest.fn();
+    describe('without labelNames feature toggle', () => {
+      const lokiLabelNamesQueryApi = config.featureToggles.lokiLabelNamesQueryApi;
+      beforeAll(() => {
+        config.featureToggles.lokiLabelNamesQueryApi = false;
+      });
+      afterAll(() => {
+        config.featureToggles.lokiLabelNamesQueryApi = lokiLabelNamesQueryApi;
+      });
 
-      const instance = new LanguageProvider(datasourceWithLabels);
-      instance.request = jest.fn();
-      await instance.fetchLabels({ streamSelector: '{foo="bar"}' });
-      expect(instance.request).toHaveBeenCalledWith('series', {
-        end: 1560163909000,
-        'match[]': '{foo="bar"}',
-        start: 1560153109000,
+      it('should use series endpoint for request with stream selector', async () => {
+        const datasourceWithLabels = setup({});
+        datasourceWithLabels.languageProvider.request = jest.fn();
+
+        const instance = new LanguageProvider(datasourceWithLabels);
+        instance.request = jest.fn();
+        await instance.fetchLabels({ streamSelector: '{foo="bar"}' });
+        expect(instance.request).toHaveBeenCalledWith('series', {
+          end: 1560163909000,
+          'match[]': '{foo="bar"}',
+          start: 1560153109000,
+        });
+      });
+    });
+
+    describe('with labelNames feature toggle', () => {
+      const lokiLabelNamesQueryApi = config.featureToggles.lokiLabelNamesQueryApi;
+      beforeAll(() => {
+        config.featureToggles.lokiLabelNamesQueryApi = true;
+      });
+      afterAll(() => {
+        config.featureToggles.lokiLabelNamesQueryApi = lokiLabelNamesQueryApi;
+      });
+
+      it('should use series endpoint for request with stream selector', async () => {
+        const datasourceWithLabels = setup({});
+        datasourceWithLabels.languageProvider.request = jest.fn();
+
+        const instance = new LanguageProvider(datasourceWithLabels);
+        instance.request = jest.fn();
+        await instance.fetchLabels({ streamSelector: '{foo="bar"}' });
+        expect(instance.request).toHaveBeenCalledWith('labels', {
+          end: 1560163909000,
+          query: '{foo="bar"}',
+          start: 1560153109000,
+        });
       });
     });
 

public/app/plugins/datasource/loki/LanguageProvider.ts

@@ -147,8 +147,8 @@ export default class LokiLanguageProvider extends LanguageProvider {
    * @throws An error if the fetch operation fails.
    */
   async fetchLabels(options?: { streamSelector?: string; timeRange?: TimeRange }): Promise<string[]> {
-    // If there is no stream selector - use /labels endpoint (https://github.com/grafana/loki/pull/11982)
-    if (!options || !options.streamSelector) {
+    // We'll default to use `/labels`. If the flag is disabled, and there's a streamSelector, we'll use the series endpoint.
+    if (config.featureToggles.lokiLabelNamesQueryApi || !options?.streamSelector) {
       return this.fetchLabelsByLabelsEndpoint(options);
     } else {
       const data = await this.fetchSeriesLabels(options.streamSelector, { timeRange: options.timeRange });
@@ -166,14 +166,20 @@ export default class LokiLanguageProvider extends LanguageProvider {
    * @returns A promise containing an array of label keys.
    * @throws An error if the fetch operation fails.
    */
-  private async fetchLabelsByLabelsEndpoint(options?: { timeRange?: TimeRange }): Promise<string[]> {
+  private async fetchLabelsByLabelsEndpoint(options?: {
+    streamSelector?: string;
+    timeRange?: TimeRange;
+  }): Promise<string[]> {
     const url = 'labels';
     const range = options?.timeRange ?? this.getDefaultTimeRange();
-    const timeRange = this.datasource.getTimeRangeParams(range);
-
-    const res = await this.request(url, timeRange);
+    const { start, end } = this.datasource.getTimeRangeParams(range);
+    const params: Record<string, string | number> = { start, end };
+    if (options?.streamSelector) {
+      params['query'] = options.streamSelector;
+    }
+    const res = await this.request(url, params);
     if (Array.isArray(res)) {
-      const labels = res
+      const labels = Array.from(new Set(res))
         .slice()
         .sort()
         .filter((label: string) => label.startsWith('__') === false);