MQE: only reduce resolution of delta in rate and increase once (#…

…9531)

* Only reduce resolution of delta once if schema changes multiple times in range

* Add changelog entry

CHANGELOG.md

@@ -14,7 +14,7 @@
   * `cortex_alertmanager_alerts`
   * `cortex_alertmanager_silences`
 * [CHANGE] Cache: Deprecate experimental support for Redis as a cache backend. #9453
-* [FEATURE] Querier: add experimental streaming PromQL engine, enabled with `-querier.query-engine=mimir`. #9367 #9368 #9398 #9399 #9403 #9417 #9418 #9419 #9420 #9482 #9504 #9505 #9507 #9518 #9532 #9533
+* [FEATURE] Querier: add experimental streaming PromQL engine, enabled with `-querier.query-engine=mimir`. #9367 #9368 #9398 #9399 #9403 #9417 #9418 #9419 #9420 #9482 #9504 #9505 #9507 #9518 #9531 #9532 #9533
 * [FEATURE] Query-frontend: added experimental configuration options `query-frontend.cache-errors` and `query-frontend.results-cache-ttl-for-errors` to allow non-transient responses to be cached. When set to `true` error responses from hitting limits or bad data are cached for a short TTL. #9028
 * [FEATURE] gRPC: Support S2 compression. #9322
   * `-alertmanager.alertmanager-client.grpc-compression=s2`

pkg/streamingpromql/functions/rate_increase.go

@@ -84,17 +84,17 @@ func histogramRate(isRate bool, step types.RangeVectorStepData, hHead []promql.H
 		emitAnnotation(annotations.NewNativeHistogramNotCounterWarning)
 	}
 
-	initialSchema := firstPoint.H.Schema
-	if lastPoint.H.Schema < initialSchema {
-		initialSchema = lastPoint.H.Schema
+	desiredSchema := firstPoint.H.Schema
+	if lastPoint.H.Schema < desiredSchema {
+		desiredSchema = lastPoint.H.Schema
 	}
 
 	usingCustomBuckets := firstPoint.H.UsesCustomBuckets()
 	if lastPoint.H.UsesCustomBuckets() != usingCustomBuckets {
 		return nil, histogram.ErrHistogramsIncompatibleSchema
 	}
 
-	delta := lastPoint.H.CopyToSchema(initialSchema)
+	delta := lastPoint.H.CopyToSchema(desiredSchema)
 	_, err := delta.Sub(firstPoint.H)
 	if err != nil {
 		return nil, err
@@ -114,8 +114,8 @@ func histogramRate(isRate bool, step types.RangeVectorStepData, hHead []promql.H
 				return histogram.ErrHistogramsIncompatibleSchema
 			}
 
-			if p.H.Schema < delta.Schema {
-				delta = delta.CopyToSchema(p.H.Schema)
+			if p.H.Schema < desiredSchema {
+				desiredSchema = p.H.Schema
 			}
 
 			if p.H.CounterResetHint == histogram.GaugeType {
@@ -138,6 +138,10 @@ func histogramRate(isRate bool, step types.RangeVectorStepData, hHead []promql.H
 
 	}
 
+	if delta.Schema != desiredSchema {
+		delta = delta.CopyToSchema(desiredSchema)
+	}
+
 	val := calculateHistogramRate(isRate, step.RangeStart, step.RangeEnd, rangeSeconds, firstPoint, lastPoint, delta, hCount)
 	return val, err
 }