Prometheus: disable dynamic label lookup on big datasources (#20936)

* Prometheus: disable dynamic label lookup on big datasources

- when a prometheus datasource has more than 10000 metrics, label lookup
for the query field is disabled
- installations of that size have slow typehead lookup times and make
the editor sluggish

* Raise dynamic lookup threshold to 10000 metrics

* Run start tasks again

public/app/plugins/datasource/prometheus/components/PromQueryField.tsx

@@ -23,7 +23,6 @@ import { PrometheusDatasource } from '../datasource';
 import PromQlLanguageProvider from '../language_provider';
 
 const HISTOGRAM_GROUP = '__histograms__';
-const METRIC_MARK = 'metric';
 const PRISM_SYNTAX = 'promql';
 export const RECORDING_RULES_GROUP = '__recording_rules__';
 
@@ -138,6 +137,7 @@ class PromQueryField extends React.PureComponent<PromQueryFieldProps, PromQueryF
 
   componentDidMount() {
     if (this.languageProvider) {
+      Prism.languages[PRISM_SYNTAX] = this.languageProvider.syntax;
       this.refreshMetrics(makePromiseCancelable(this.languageProvider.start()));
     }
     this.refreshHint();
@@ -228,17 +228,11 @@ class PromQueryField extends React.PureComponent<PromQueryFieldProps, PromQueryF
   };
 
   onUpdateLanguage = () => {
-    const { histogramMetrics, metrics } = this.languageProvider;
+    const { histogramMetrics, metrics, lookupsDisabled, lookupMetricsThreshold } = this.languageProvider;
     if (!metrics) {
       return;
     }
 
-    Prism.languages[PRISM_SYNTAX] = this.languageProvider.syntax;
-    Prism.languages[PRISM_SYNTAX][METRIC_MARK] = {
-      alias: 'variable',
-      pattern: new RegExp(`(?:^|\\s)(${metrics.join('|')})(?:$|\\s)`),
-    };
-
     // Build metrics tree
     const metricsByPrefix = groupMetricsByPrefix(metrics);
     const histogramOptions = histogramMetrics.map((hm: any) => ({ label: hm, value: hm }));
@@ -250,7 +244,16 @@ class PromQueryField extends React.PureComponent<PromQueryFieldProps, PromQueryF
           ]
         : metricsByPrefix;
 
-    this.setState({ metricsOptions, syntaxLoaded: true });
+    // Hint for big disabled lookups
+    let hint: QueryHint;
+    if (lookupsDisabled) {
+      hint = {
+        label: `Dynamic label lookup is disabled for datasources with more than ${lookupMetricsThreshold} metrics.`,
+        type: 'INFO',
+      };
+    }
+
+    this.setState({ hint, metricsOptions, syntaxLoaded: true });
   };
 
   onTypeahead = async (typeahead: TypeaheadInput): Promise<TypeaheadOutput> => {