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new f7be683a45c Adjust cost-based autoscaler constant for lag
multiplication (#19045)
f7be683a45c is described below
commit f7be683a45c36020198520336a26d17d1ba18be7
Author: Sasha Syrotenko <[email protected]>
AuthorDate: Tue Feb 24 11:10:17 2026 +0200
Adjust cost-based autoscaler constant for lag multiplication (#19045)
---
.../seekablestream/supervisor/autoscaler/WeightedCostFunction.java | 6 +++++-
.../supervisor/autoscaler/WeightedCostFunctionTest.java | 4 ++--
2 files changed, 7 insertions(+), 3 deletions(-)
diff --git
a/indexing-service/src/main/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/WeightedCostFunction.java
b/indexing-service/src/main/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/WeightedCostFunction.java
index 2fbb365fb99..0f5ea6083c7 100644
---
a/indexing-service/src/main/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/WeightedCostFunction.java
+++
b/indexing-service/src/main/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/WeightedCostFunction.java
@@ -29,7 +29,11 @@ import org.apache.druid.java.util.common.logger.Logger;
public class WeightedCostFunction
{
private static final Logger log = new Logger(WeightedCostFunction.class);
- private static final double LAG_AMPLIFICATION_MULTIPLIER = 0.2;
+ /**
+ * Multiplier for a lag amplification factor; it was carefully chosen
+ * during extensive testing as the most balanced multiplier for high-lag
recovery.
+ */
+ static final double LAG_AMPLIFICATION_MULTIPLIER = 0.05;
/**
* Computes cost for a given task count using compute time metrics.
diff --git
a/indexing-service/src/test/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/WeightedCostFunctionTest.java
b/indexing-service/src/test/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/WeightedCostFunctionTest.java
index c4d4f493498..c4133c0093b 100644
---
a/indexing-service/src/test/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/WeightedCostFunctionTest.java
+++
b/indexing-service/src/test/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/WeightedCostFunctionTest.java
@@ -97,7 +97,7 @@ public class WeightedCostFunctionTest
// aggregateLag = 100000 * 100 = 10,000,000; lagPerPartition = 100,000
CostMetrics metrics = createMetrics(100000.0, 10, 100, 0.3);
double aggregateLag = 100000.0 * 100;
- double amplification = 1.0 + 0.2 * Math.log(aggregateLag / 100);
+ double amplification = 1.0 +
WeightedCostFunction.LAG_AMPLIFICATION_MULTIPLIER * Math.log(aggregateLag /
100);
double costCurrent = costFunction.computeCost(metrics, 10,
lagOnlyConfig).totalCost();
Assert.assertEquals("Cost of current tasks", aggregateLag * amplification
/ (10 * 1000.0), costCurrent, 0.1);
@@ -307,7 +307,7 @@ public class WeightedCostFunctionTest
double aggregateLag = 150.0 * partitionCount;
double lagPerPartition = aggregateLag / partitionCount;
- double amplification = 1.0 + 0.2 * Math.log(lagPerPartition);
+ double amplification = 1.0 +
WeightedCostFunction.LAG_AMPLIFICATION_MULTIPLIER * Math.log(lagPerPartition);
double expected = aggregateLag * amplification / (proposedTaskCount *
1000.0);
Assert.assertEquals("Lag amplification should increase lag recovery time",
expected, costWithAmp, 0.0001);
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