FrankChen021 commented on code in PR #19697:
URL: https://github.com/apache/druid/pull/19697#discussion_r3595287442
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indexing-service/src/main/java/org/apache/druid/indexing/seekablestream/supervisor/autoscaler/CostBasedAutoScaler.java:
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@@ -326,6 +330,15 @@ int computeOptimalTaskCount(CostMetrics metrics)
);
emitter.emit(getMetricBuilder().setMetric(OPTIMAL_LAG_COST_METRIC,
optimalCost.lagCost()));
emitter.emit(getMetricBuilder().setMetric(OPTIMAL_IDLE_COST_METRIC,
optimalCost.idleCost()));
+
+ final double costDropPercent = (currentCost.totalCost() -
optimalCost.totalCost()) / currentCost.totalCost();
+ if (costDropPercent < config.getMinCostDropPercentForScaling()) {
Review Comment:
[P1] Compare the cost drop in percentage units
`costDropPercent` is currently a fraction in the range 0-1, while the
integer configuration represents a percentage (the added serde test uses `10`).
Consequently, configuring a 10% threshold makes every possible improvement
compare below 10 and disables all scaling; even a value of 1 requires a full
100% cost reduction. Multiply the computed ratio by 100 or normalize the
configured value before comparing, and add a scaling-behavior test for a
nonzero threshold.
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