apache/cassandra · error · IllegalArgumentException

Invalid latency modifier specification

Error message

Invalid latency modifier specification: {spec}. Expect constant factor as base for exponent.

What it means

Thrown by TimeoutStrategy.parseLatencyModifier when a latency modifier clause in a timeout specification begins with a modifier kind that is neither null nor a '*' factor; only constant factors (base for exponent) are accepted at this position.

Solutions

Use a plain numeric constant (e.g. '2') or a '*'-prefixed factor (e.g. '*2') for the modifier.
Move the '^' exponent syntax to the attempts-modifier position where it is accepted.
Check the spec against the PARSE regex pattern documented in TimeoutStrategy.

Example fix

// before
String spec = "fixed*^2"; // invalid: '^' where a factor is expected
// after
String spec = "fixed*2";   // or use '...^2' in the attempts-modifier position

Defensive patterns

Strategy: validation

Validate before calling

if (spec != null && spec.matches(".*[^*\d.]\^?.*")) { /* validate against PARSE regex before passing */ }
// simpler: reject '^' at the modifier position
java.util.regex.Pattern p = java.util.regex.Pattern.compile(".*\\*?\\d+(\\.\\d+)?$");

Try / catch

try { TimeoutStrategy.parse(spec, latencies); }
catch (IllegalArgumentException e) { if (e.getMessage().contains("Invalid latency modifier")) { /* correct modifier syntax */ } throw e; }

Prevention

Use plain numbers or '*' factors at the modifier position
Reserve '^' for the attempts-modifier position only
Test spec strings in a staging config first

When it happens

Trigger: Passing a timeout/latency spec string whose modifier segment uses an unsupported prefix, e.g. '^' alone or other characters, where a plain numeric factor or '*' factor is expected.

Common situations: Hand-editing cassandra timeout config strings (e.g. read/request timeout expressions) with invalid modifier syntax; confusing '^' (attempts exponent) with the base factor position.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/650ab6aa6d00ea13. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/service/TimeoutStrategy.java:321

        if (perc == null)
            return new Constant(parseInMicros(m.group("constbase")));

        String rw = m.group("rw");
        if (rw == null) rw = "rw";
        LatencySource latencies = latenciesFactory.source(rw);
        double percentile = parseDouble("0." + perc);
        return new Percentile(latencies, percentile);
    }

    private static @Nullable LatencyModifier parseLatencyModifier(String spec, Matcher m, LatencyModifierFactory modifiers)
    {
        String mod = m.group("mod");
        String modkind = m.group("modkind");
        double modifier = 1.0;
        if (mod != null) modifier = Double.parseDouble(mod);
        else if (modkind == null) return null;
        else if (!modkind.startsWith("*"))
            throw new IllegalArgumentException("Invalid latency modifier specification: " + spec + ". Expect constant factor as base for exponent.");

        if (modkind == null)
            return modifiers.multiply(modifier);

        if (modkind.startsWith("*"))
            return modifiers.multiplyByAttempts(modifier);
        else if (modkind.startsWith("^"))
            return modifiers.multiplyByAttemptsExp(modifier);
        else
            throw new IllegalArgumentException("Unrecognised attempt modifier: " + modkind);
    }

    static long saturatedCast(double v)
    {
        if (v > Long.MAX_VALUE)
            return Long.MAX_VALUE;
        return (long) v;
    }

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