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CNDB-15794: Allow ShardingStats to be propagated in CNDB #2487

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CNDB-15794: Allow ShardingStats to be propagated in CNDB #2487

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63b9e6a
CNDB-15794: Allow ShardingStats to be propagated in CNDB
lesnik2u Jun 24, 2026
4d313d1
CNDB-18245: Remove VisibleForTesting annotation and add cloneWithAdju…
lesnik2u Jul 2, 2026
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40 changes: 37 additions & 3 deletions src/java/org/apache/cassandra/db/compaction/UnifiedCompactionStrategy.java
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Original file line number Diff line number Diff line change
Expand Up @@ -581,9 +581,12 @@ public ShardingStats(Collection<? extends CompactionSSTable> sstables, Range<Tok
this.coveredShardCount = shardManager.coveredShardCount(min, max, shardCountForDensity);
}

/// Testing only, use specified values.
@VisibleForTesting
ShardingStats(PartitionPosition min, PartitionPosition max, long totalOnDiskSize, double overheadToDataRatio, double uniqueKeyRatio, double density, int shardCountForDensity, int coveredShardCount)
/**
* Reconstructs sharding statistics using the specified density and shard counts.
* Used by CNDB to propagate pre-computed density from the leader to follower compactor nodes,
* and for testing.
*/
public ShardingStats(PartitionPosition min, PartitionPosition max, long totalOnDiskSize, double overheadToDataRatio, double uniqueKeyRatio, double density, int shardCountForDensity, int coveredShardCount)
{

this.min = min;
Expand All @@ -595,6 +598,37 @@ public ShardingStats(Collection<? extends CompactionSSTable> sstables, Range<Tok
this.shardCountForDensity = shardCountForDensity;
this.coveredShardCount = coveredShardCount;
}

/**
* Clones this {@link ShardingStats} with an adjusted density, recomputing
* the shard counts based on the new density.
*
* @param density the new sharding density to apply, must be non-negative
* @param shardManager the {@link ShardManager} to calculate shard set coverage
* @param controller the {@link Controller} to determine the number of shards
* @return a new {@link ShardingStats} instance with the adjusted density
* @throws IllegalArgumentException if {@code density} is negative
* @throws NullPointerException if {@code shardManager} or {@code controller} is null
*/
public ShardingStats cloneWithAdjustedDensity(double density, ShardManager shardManager, Controller controller)
{
Preconditions.checkArgument(density >= 0.0, "Density must be non-negative, but was %s", density);
Preconditions.checkNotNull(shardManager, "shardManager must not be null");
Preconditions.checkNotNull(controller, "controller must not be null");

int shardCountForDensity = controller.getNumShards(density * shardManager.shardSetCoverage());
int coveredShardCount = shardManager.coveredShardCount(this.min, this.max, shardCountForDensity);
return new ShardingStats(
this.min,
this.max,
this.totalOnDiskSize,
this.overheadToDataRatio,
this.uniqueKeyRatio,
density,
shardCountForDensity,
coveredShardCount
);
}
}

/// Get and store the sharding stats for a given aggregate
Expand Down