apache/cassandra · error · IllegalArgumentException

Invalid specification:

Error message

Invalid  specification: 

What it means

OptionMulti parses a compound spec (like a compound 'key=value,rate' list, e.g. 'read=1,write=2') with a regex and requires the tokens to be contiguous matches. When a token starts at a position other than lastEnd+1, the whole parameter is malformed (stray characters between comma-separated parts), producing 'Invalid <name> specification: <param>'.

Solutions

1. Remove stray characters so tokens are contiguous and comma-separated: read=1,write=2
2. Quote the whole spec for the shell and avoid internal spaces
3. Test the spec string against the expected '<name>=<value>[,...]' pattern before invoking.

Example fix

// before
-read=1,,write=2
// after
-read=1,write=2

boolean wellFormed(String spec){ return spec.matches("([A-Za-z_]+=\\d+)(,[A-Za-z_]+=\\d+)*"); } // contiguous, comma-separated key=value

try { opt.accept(spec); } catch (IllegalArgumentException e) { log.error("Malformed compound spec '{}'", spec); }

When it happens

Trigger: A spec string with stray/unrecognized characters between recognized tokens, e.g. 'read=1,,write=2' or 'read=1; write=2', so the matcher finds a gap.

Common situations: Double commas from template substitution; using ';' instead of ','; spaces inside the spec that the regex treats as noise; copied specs with invisible characters.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• arguments for -F are json, yaml, table only.
• Cannot specify tokens without keyspace.
• Invalid parameter list for fixed distribution:
• Invalid parameter list for sequence distribution:
• Invalid parameter list for sequence distribution…

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/ce528daa5dec8f40. Report an issue: GitHub.

Appendix: source

Thrown at tools/stress/src/org/apache/cassandra/stress/settings/OptionMulti.java:87

    {
        this.name = name;
        pattern = Pattern.compile(name + "\\((.*)\\)", Pattern.CASE_INSENSITIVE);
        this.description = description;
        this.collectAsMap = collectExtraOptionsInMap ? new CollectAsMap() : null;
    }

    @Override
    public boolean accept(String param)
    {
        Matcher m = pattern.matcher(param);
        if (!m.matches())
            return false;
        m = ARGS.matcher(m.group(1));
        int last = -1;
        while (m.find())
        {
            if (m.start() != last + 1)
                throw new IllegalArgumentException("Invalid " + name + " specification: " + param);
            last = m.end();
            if (!delegate.accept(m.group()))
            {

                throw new IllegalArgumentException("Invalid " + name + " specification: " + m.group());
            }
        }
        return true;
    }

    public String toString()
    {
        StringBuilder sb = new StringBuilder();
        sb.append(name);
        sb.append("(");
        for (Option option : delegate.options())
        {
            sb.append(option);

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