apache/cassandra · error · IllegalArgumentException

can't have both fixed and throttle set, choose one.

Error message

can't have both fixed and throttle set, choose one.

What it means

SettingsRate lets you limit throughput either with -rate throttle=<N>/s (dynamic rate limiting) or -rate fixed=<N>/s (fixed rate), but not both. The constructor throws IllegalArgumentException when both parse to non-zero values because the two modes are mutually exclusive.

Solutions

1. Keep only one of throttle= or fixed= in the -rate option
2. If you want a strict fixed rate, drop throttle=; if you want adaptive throttling, drop fixed=
3. threads= can be combined with either one, so keep threads and one rate knob

Example fix

// before
-rate threads=10 throttle=5000/s fixed=3000/s
// after
-rate threads=10 throttle=5000/s

boolean hasThrottle = cmdLine.matches(".*-rate[^-]*throttle=[^0]");
boolean hasFixed = cmdLine.matches(".*-rate[^-]*fixed=[^0]");
if (hasThrottle && hasFixed) throw new IllegalArgumentException("choose either throttle or fixed");

try { SettingsRate.get(clArgs, cmd); } catch (IllegalArgumentException e) { if (e.getMessage().contains("both fixed and throttle")) stripOption(args, "fixed"); else throw e; }

When it happens

Trigger: cassandra-stress ... -rate threads=10 throttle=5000/s fixed=3000/s — both throttle and fixed options supplied with non-zero values.

Common situations: Merging rate settings from two script fragments, or a template command that already contains fixed= while the operator appends throttle=.

Related errors

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AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/774b3d0427ba07aa. Report an issue: GitHub.

Appendix: source

Thrown at tools/stress/src/org/apache/cassandra/stress/settings/SettingsRate.java:50

{

    public final boolean auto;
    public final int minThreads;
    public final int maxThreads;
    public final int threadCount;
    public final int opsPerSecond;
    public final boolean isFixed;

    public SettingsRate(ThreadOptions options)
    {
        auto = false;
        threadCount = Integer.parseInt(options.threads.value());
        String throttleOpt = options.throttle.value();
        String fixedOpt = options.fixed.value();
        int throttle = Integer.parseInt(throttleOpt.substring(0, throttleOpt.length() - 2));
        int fixed = Integer.parseInt(fixedOpt.substring(0, fixedOpt.length() - 2));
        if(throttle != 0 && fixed != 0)
            throw new IllegalArgumentException("can't have both fixed and throttle set, choose one.");
        opsPerSecond = Math.max(fixed, throttle);
        isFixed = (opsPerSecond == fixed);

        minThreads = -1;
        maxThreads = -1;
    }

    public SettingsRate(AutoOptions auto)
    {
        this.auto = auto.auto.setByUser();
        this.minThreads = Integer.parseInt(auto.minThreads.value());
        this.maxThreads = Integer.parseInt(auto.maxThreads.value());
        this.threadCount = -1;
        this.opsPerSecond = 0;
        isFixed = false;
    }

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