kfaraz commented on code in PR #18991:
URL: https://github.com/apache/druid/pull/18991#discussion_r2786303734


##########
indexing-service/src/main/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/WeightedCostFunction.java:
##########
@@ -73,12 +68,19 @@ public CostResult computeCost(
       }
     } else {
       // Lag recovery time is decreasing by adding tasks and increasing by 
ejecting tasks.
+      // In case of increasing lag, we apply an amplification factor to 
reflect the urgency of addressing lag.
       // Caution: we rely only on the metrics, the real issues may be 
absolutely different, up to hardware failure.
-      lagRecoveryTime = metrics.getAggregateLag() / (proposedTaskCount * 
avgProcessingRate);
+      if (metrics.getAggregateLag() <= 0) {
+        lagRecoveryTime = 0;
+      } else {
+        final double lagPerPartition = metrics.getAggregateLag() / 
metrics.getPartitionCount();
+        final double amplification = Math.max(1.0, 1.0 + 
LAG_AMPLIFICATION_MULTIPLIER * Math.log(lagPerPartition));

Review Comment:
   I see. Would it be possible to see how the autoscaler does without the 
amplification?
   Could that be an option?



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