Rename cacheKey to exprID/requestID

Depending on context in the code, rename cacheKey
to exprID when it identifies a unique expression,
and rename cacheKey to requestID when it is
identifying a request.

public/app/core/services/backend_srv.js

@@ -96,18 +96,18 @@ function (angular, _, coreModule, config) {
     this.datasourceRequest = function(options) {
       options.retry = options.retry || 0;
 
-      // A cacheKey is provided by the datasource as a unique identifier for a
-      // particular query. If the cacheKey exists, the promise it is keyed to
+      // A requestID is provided by the datasource as a unique identifier for a
+      // particular query. If the requestID exists, the promise it is keyed to
       // is canceled, canceling the previous datasource request if it is still
       // in-flight.
       var canceler;
-      if (options.cacheKey) {
-        if (canceler = datasourceInFlightRequests[options.cacheKey]) {
+      if (options.requestID) {
+        if (canceler = datasourceInFlightRequests[options.requestID]) {
           canceler.resolve();
         }
         canceler = $q.defer();
         options.timeout = canceler.promise;
-        datasourceInFlightRequests[options.cacheKey] = canceler;
+        datasourceInFlightRequests[options.requestID] = canceler;
       }
 
       var requestIsLocal = options.url.indexOf('/') === 0;

public/app/features/panel/metrics_panel_ctrl.ts

@@ -183,7 +183,7 @@ class MetricsPanelCtrl extends PanelCtrl {
     };
 
     metricsQuery.targets.forEach(function(target) {
-      target.cacheKey = target.expr + target.refId + metricsQuery.panelId;
+      target.exprID = target.expr + target.refId + metricsQuery.panelId;
     });
 
     return datasource.query(metricsQuery);

public/app/plugins/datasource/prometheus/datasource.ts

@@ -21,11 +21,11 @@ export function PrometheusDatasource(instanceSettings, $q, backendSrv, templateS
   this.withCredentials = instanceSettings.withCredentials;
   this.lastErrors = {};
 
-  this._request = function(method, url, cacheKey) {
+  this._request = function(method, url, requestID) {
     var options: any = {
       url: this.url + url,
       method: method,
-      cacheKey: cacheKey,
+      requestID: requestID,
     };
 
     if (this.basicAuth || this.withCredentials) {
@@ -77,7 +77,7 @@ export function PrometheusDatasource(instanceSettings, $q, backendSrv, templateS
 
       var query: any = {};
       query.expr = templateSrv.replace(target.expr, options.scopedVars, self.interpolateQueryExpr);
-      query.cacheKey = target.cacheKey;
+      query.requestID = target.exprID;
 
       var interval = target.interval || options.interval;
       var intervalFactor = target.intervalFactor || 1;
@@ -128,7 +128,7 @@ export function PrometheusDatasource(instanceSettings, $q, backendSrv, templateS
 
   this.performTimeSeriesQuery = function(query, start, end) {
     var url = '/api/v1/query_range?query=' + encodeURIComponent(query.expr) + '&start=' + start + '&end=' + end + '&step=' + query.step;
-    return this._request('GET', url, query.cacheKey);
+    return this._request('GET', url, query.requestID);
   };
 
   this.performSuggestQuery = function(query) {