apache/cassandra · warning · RuntimeException

Use the -d flag to quiet this error and get the exact…

Error message

Use the -d flag to quiet this error and get the exact throughput in MiB/s

What it means

GetCompactionThroughput prints the throughput as an integer when -d is absent; if the configured compaction throughput is a non-integer MiB/s value, it throws this RuntimeException telling the operator to use -d. It protects against silently rounding the value.

Solutions

Run `nodetool getcompactionthroughput -d` to print the exact double value
Set compaction_throughput_mb_per_sec to an integer in cassandra.yaml
Update monitoring scripts to pass -d and parse a double

Example fix

// before
nodetool getcompactionthroughput
// after
nodetool getcompactionthroughput -d

Defensive patterns

Strategy: validation

Validate before calling

// pass -d whenever fractional values are possible
nodetool getcompactionthroughput -d

Try / catch

try { probe.execute(); } catch (RuntimeException e) { if (e.getMessage().contains("-d flag")) retryWithDoubleFlag(); }

Prevention

Always use -d in automation
Keep compaction_throughput_mb_per_sec an integer if scripts rely on integer output
Parse output as double

When it happens

Trigger: Running `nodetool getcompactionthroughput` when compaction_throughput_mb_per_sec in cassandra.yaml is set to a fractional value (e.g. 63.5) without the -d flag.

Common situations: Operators set fractional throughput values for tuning; monitoring scripts parse output and break on the thrown error; versions where the setting became a double.

Understand the failure class

Background: "unknown output mode", "invalid value for flag", "expects true/false": fixing invalid flag value errors in CLI tools — this error's family across 24 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/f880c8d44b0229dd. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/tools/nodetool/GetCompactionThroughput.java:45

import picocli.CommandLine.Option;

@Command(name = "getcompactionthroughput", description = "Print the MiB/s throughput cap for compaction in the system as a rounded number")
public class GetCompactionThroughput extends AbstractCommand
{
    @Option(names = { "-d", "--precise-mib" }, description = "Print the MiB/s throughput cap for compaction in the system as a precise number (double)")
    private boolean  compactionThroughputAsDouble;

    @Override
    public void execute(NodeProbe probe)
    {
        double throughput = probe.getCompactionThroughputMebibytesAsDouble();

        if (compactionThroughputAsDouble)
            probe.output().out.println("Current compaction throughput: " + throughput + " MiB/s");
        else
        {
            if (!DoubleMath.isMathematicalInteger(throughput))
                throw new RuntimeException("Use the -d flag to quiet this error and get the exact throughput in MiB/s");

            probe.output().out.println("Current compaction throughput: " + probe.getCompactionThroughput() + " MiB/s");
        }

        Map<String, String> currentCompactionThroughputMetricsMap = probe.getCurrentCompactionThroughputMiBPerSec();
        probe.output().out.println("Current compaction throughput (1 minute): " + currentCompactionThroughputMetricsMap.get("1minute") + " MiB/s");
        probe.output().out.println("Current compaction throughput (5 minute): " + currentCompactionThroughputMetricsMap.get("5minute") + " MiB/s");
        probe.output().out.println("Current compaction throughput (15 minute): " + currentCompactionThroughputMetricsMap.get("15minute") + " MiB/s");
    }
}

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