apache/cassandra · error · IllegalArgumentException

is defined multiple times. Each option/command can be…

Error message

 is defined multiple times. Each option/command can be specified at most once.

What it means

The stress CLI parses arguments into a map keyed by option/command name; putParam throws IllegalArgumentException when the same key is seen a second time, since each option or command may be specified at most once on the command line.

Solutions

1. Remove duplicate occurrences of the named option from the command line
2. Combine values into a single occurrence where the option accepts lists, e.g. -node ip1,ip2 or -log interval=10s level=debug
3. Fix the script that builds the arguments to deduplicate flags

Example fix

// before
-node 127.0.0.1 -node 127.0.0.2
// after
-node 127.0.0.1,127.0.0.2

Map<String,Integer> seen = new HashMap<>();
for (String a : args) if (a.startsWith("-")) {
  int n = seen.merge(a, 1, Integer::sum);
  if (n > 1) throw new IllegalArgumentException(a + " repeated");
}

try { StressSettings.get(parseMap(rawArgs)); } catch (IllegalArgumentException e) { if (e.getMessage().endsWith("defined multiple times")) { dedupe(rawArgs); retry(); } else throw e; }

When it happens

Trigger: Repeating any option or command, e.g. 'cassandra-stress write -log interval=10s -log level=debug' or '-node a -node b' — the second occurrence triggers the error naming the duplicated key.

Common situations: Concatenating option strings from multiple config sources in scripts, shell loops appending the same flag per item instead of comma-joining values.

Understand the failure class

Background: "Unknown argument", "Invalid value", and "must be one of": invalid CLI argument errors explained — this error's family across 35 libraries.

Related errors

• can't have both fixed and throttle set, choose one.
• Log interval must be greater than zero
• -schema can only be provided with predefined operations…
• Suboption has been specified more than once
• A repair_session_space of

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/0e3c4ab5f921dcfe. Report an issue: GitHub.

Appendix: source

Thrown at tools/stress/src/org/apache/cassandra/stress/settings/StressSettings.java:269

            if (i == 0 || args[i].startsWith("-"))
            {
                if (i > 0)
                    putParam(key, params.toArray(new String[0]), r);
                key = toLowerCaseLocalized(args[i]);
                params.clear();
            }
            else
                params.add(args[i]);
        }
        putParam(key, params.toArray(new String[0]), r);
        return r;
    }

    private static void putParam(String key, String[] args, Map<String, String[]> clArgs)
    {
        String[] prev = clArgs.put(key, args);
        if (prev != null)
            throw new IllegalArgumentException(key + " is defined multiple times. Each option/command can be specified at most once.");
    }

    public static void printHelp()
    {
        SettingsMisc.printHelp();
    }

    public void printSettings(ResultLogger out)
    {
        out.println("******************** Stress Settings ********************");
        // done
        out.println("Command:");
        command.printSettings(out);
        out.println("Rate:");
        rate.printSettings(out);
        out.println("Population:");
        generate.printSettings(out);
        out.println("Insert:");

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