GEL: wrap arrow utils in async load (#20134)

public/app/features/expressions/ExpressionDatasource.ts

@@ -10,10 +10,9 @@ import { ExpressionQueryEditor } from './ExpressionQueryEditor';
 import { Observable, from } from 'rxjs';
 import { config } from '@grafana/runtime';
 import { getBackendSrv } from 'app/core/services/backend_srv';
-import { gelResponseToDataFrames } from './util';
 
 /**
- * This is a singleton that is not actually instanciated
+ * This is a singleton that is not actually instantiated
  */
 export class ExpressionDatasourceApi extends DataSourceApi<ExpressionQuery> {
   constructor(instanceSettings: DataSourceInstanceSettings) {
@@ -53,11 +52,19 @@ export class ExpressionDatasourceApi extends DataSourceApi<ExpressionQuery> {
         queries: queries,
       })
       .then((rsp: any) => {
-        return { data: gelResponseToDataFrames(rsp) } as DataQueryResponse;
+        return this.toDataQueryResponse(rsp);
       });
     return from(req);
   }
 
+  /**
+   * This makes the arrow libary loading async.
+   */
+  async toDataQueryResponse(rsp: any): Promise<DataQueryResponse> {
+    const { gelResponseToDataFrames } = await import(/* webpackChunkName: "apache-arrow-util" */ './util');
+    return { data: gelResponseToDataFrames(rsp) };
+  }
+
   testDatasource() {
     return Promise.resolve({});
   }

public/app/features/expressions/util.ts

@@ -1,7 +1,7 @@
 import { DataFrame, FieldType, Field, Vector } from '@grafana/data';
 import { Table, ArrowType } from 'apache-arrow';
 
-export function base64StringToArrowTable(text: string) {
+export function base64StringToArrowTable(text: string): Table {
   const b64 = atob(text);
   const arr = Uint8Array.from(b64, c => {
     return c.charCodeAt(0);