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CNDB-16026: CNDB-15971: Only init ReadExecutionController's histogram when tracing on #2135

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CNDB-16026: CNDB-15971: Only init ReadExecutionController's histogram when tracing on #2135

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14 changes: 10 additions & 4 deletions src/java/org/apache/cassandra/db/ReadExecutionController.java
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Original file line number Diff line number Diff line change
Expand Up @@ -55,7 +55,7 @@ public class ReadExecutionController implements AutoCloseable
private final RepairedDataInfo repairedDataInfo;
private long oldestUnrepairedTombstone = Long.MAX_VALUE;

public final Histogram sstablesScannedPerRowRead;
private final Histogram sstablesScannedPerRowRead;

ReadExecutionController(ReadCommand command,
OpOrder.Group baseOp,
Expand All @@ -75,7 +75,10 @@ public class ReadExecutionController implements AutoCloseable
this.command = command;
this.createdAtNanos = createdAtNanos;

this.sstablesScannedPerRowRead = new Histogram(new DecayingEstimatedHistogramReservoir(true));
// This is expensive to create, and since this is on the query hot path, we must only make it when we need it.
this.sstablesScannedPerRowRead = Tracing.isTracing()
? new Histogram(new DecayingEstimatedHistogramReservoir(true))
: null;

if (trackRepairedStatus)
{
Expand Down Expand Up @@ -228,7 +231,7 @@ public void close()
if (createdAtNanos != NO_SAMPLING)
addSample();

if (Tracing.traceSinglePartitions())
if (sstablesScannedPerRowRead != null)
{
Snapshot sstablesHistogram = sstablesScannedPerRowRead.getSnapshot();
Tracing.trace("Scanned {} rows; average {} sstables scanned per row with stdev {} and max {}",
Expand Down Expand Up @@ -272,6 +275,9 @@ private void addSample()

public void updateSstablesIteratedPerRow(int mergedSSTablesIterated)
{
sstablesScannedPerRowRead.update(mergedSSTablesIterated);
if (sstablesScannedPerRowRead != null)
{
sstablesScannedPerRowRead.update(mergedSSTablesIterated);
}
}
}