Improve log volume histogram resolution, fixes #40

Author: ddelemeny

src/datasource.ts

@@ -651,7 +651,7 @@ export function queryLogsVolume<TQuery extends DataQuery, TOptions extends DataS
   options: any
 ): Observable<DataQueryResponse> {
   const timespan = options.range.to.valueOf() - options.range.from.valueOf();
-  const intervalInfo = getIntervalInfo(logsVolumeRequest.scopedVars, timespan);
+  const intervalInfo = getIntervalInfo(timespan, 400);
 
   logsVolumeRequest.interval = intervalInfo.interval;
   logsVolumeRequest.scopedVars.__interval = { value: intervalInfo.interval, text: intervalInfo.interval };
@@ -795,32 +795,36 @@ const MINUTE = 60 * SECOND;
 const HOUR = 60 * MINUTE;
 const DAY = 24 * HOUR;
 
-function getIntervalInfo(scopedVars: ScopedVars, timespanMs: number): { interval: string; intervalMs?: number } {
-  if (scopedVars.__interval_ms) {
-    let intervalMs: number = scopedVars.__interval_ms.value;
-    let interval = '';
-    // below 5 seconds we force the resolution to be per 1ms as interval in scopedVars is not less than 10ms
-    if (timespanMs < SECOND * 5) {
-      intervalMs = MILLISECOND;
-      interval = '1ms';
-    } else if (intervalMs > HOUR) {
-      intervalMs = DAY;
-      interval = '1d';
-    } else if (intervalMs > MINUTE) {
-      intervalMs = HOUR;
-      interval = '1h';
-    } else if (intervalMs > SECOND) {
-      intervalMs = MINUTE;
-      interval = '1m';
-    } else {
-      intervalMs = SECOND;
-      interval = '1s';
-    }
 
-    return { interval, intervalMs };
+function getIntervalInfo(timespanMs: number, resolution: number): { interval: string; intervalMs?: number } {
+  let intervalMs = timespanMs / resolution;
+  let interval = '';
+
+  // below 5 seconds we force the resolution to be per 1ms as interval in scopedVars is not less than 10ms
+  if (timespanMs < SECOND * 5) {
+    intervalMs = MILLISECOND;
+    interval = '1ms';
+  } else if (intervalMs > HOUR) {
+    intervalMs = DAY;
+    interval = '1d';
+  } else if (intervalMs > 10*MINUTE) {
+    intervalMs = HOUR;
+    interval = '1h';
+  } else if (intervalMs > MINUTE) {
+    intervalMs = 10*MINUTE;
+    interval = '10m';
+  } else if (intervalMs > 10*SECOND) {
+    intervalMs = MINUTE;
+    interval = '1m';
+  } else if (intervalMs > SECOND) {
+    intervalMs = 10*SECOND;
+    interval = '10s';
   } else {
-    return { interval: '$__interval' };
+    intervalMs = SECOND;
+    interval = '1s';
   }
+
+  return { interval, intervalMs };
 }
 
 // Copy/pasted from grafana/data as it is deprecated there.