krummas commented on code in PR #4476:
URL: https://github.com/apache/cassandra/pull/4476#discussion_r2635757180
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src/java/org/apache/cassandra/db/compaction/CompactionStrategyManager.java:
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@@ -702,6 +772,89 @@ public boolean isLeveledCompaction()
}
}
+ /**
+ * Data class for accumulating UCS metrics computation state.
+ * Holds intermediate values during metric calculation across all
strategies and levels.
+ */
+ private static class CompactionStatsMetricsData
+ {
+ final double[] sum = new double[UnifiedCompactionStrategy.MAX_LEVELS];
+ final int[] count = new int[UnifiedCompactionStrategy.MAX_LEVELS];
+ final double[] max = new double[UnifiedCompactionStrategy.MAX_LEVELS];
+ int numberOfLevels = 0;
+
+ int levelIndex;
+ Level level;
+ SSTableReader sstable;
+ UnifiedCompactionStrategy strategy;
+ }
+
+ /**
+ * Generic helper to compute UCS metrics across all strategies and levels.
+ * Reduces code duplication for per-level metric calculations.
+ *
+ * @param accumulator processes each sstable and updates the metrics data
state
+ * @param finalizer computes the final result array from the accumulated
metrics data
+ * @return computed metric array, one value per level, or null if not
using UCS
+ */
+ private double[] computeUCSMetric(Consumer<CompactionStatsMetricsData>
accumulator, Function<CompactionStatsMetricsData, double[]> finalizer)
+ {
+ readLock.lock();
+ try
+ {
+ if (repaired.first() instanceof UnifiedCompactionStrategy)
+ {
+ CompactionStatsMetricsData data = new
CompactionStatsMetricsData();
+
+ for (AbstractCompactionStrategy strategy : getAllStrategies())
+ {
+ UnifiedCompactionStrategy ucsStrategy =
(UnifiedCompactionStrategy) strategy;
+ List<Level> levels = ucsStrategy.getLevelsSnapshot();
+
+ data.numberOfLevels = Math.max(data.numberOfLevels,
levels.size());
+ data.strategy = ucsStrategy;
+
+ for (int i = 0; i < levels.size(); i++)
+ {
+ data.levelIndex = i;
+ data.level = levels.get(i);
+ for (SSTableReader sstable :
levels.get(i).getSSTables())
+ {
+ data.sstable = sstable;
+ accumulator.accept(data);
+ }
+ }
+ }
+
+ return finalizer.apply(data);
+ }
+ return null;
+ }
+ finally {
+ readLock.unlock();
+ }
+ }
+
+ private static double[] averageFinalizer(CompactionStatsMetricsData data)
+ {
+ double[] res = new double[data.numberOfLevels];
+ for (int i = 0; i < data.numberOfLevels; i++)
+ res[i] = data.count[i] == 0 ? 0 : data.sum[i] /
data.numberOfLevels;
Review Comment:
this should divide by `data.count[i]`, not `numberOfLevels`
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