apache/cassandra · error · IllegalArgumentException

does not match

Error message

{input} does not match {LEGACY}

What it means

The legacy paxos contention strategy string (e.g. from paxos_contention_wait_* settings) must match the LEGACY regex (a constant or min,max[,on-failure] wait specification in time units). parseLegacy throws this IllegalArgumentException when the configured string does not conform to that grammar.

Solutions

1. Correct the contention wait string to match the legacy format: a duration constant or 'min,max' range with valid time units (e.g. '1ms,10ms')
2. Validate the setting with a local regex/test before deploying cassandra.yaml
3. Revert to defaults by removing the custom contention setting
4. Restart the node after fixing the config

Example fix

// cassandra.yaml
// before
paxos_contention_wait: 100
// after
paxos_contention_wait: 1ms,10ms

Pattern LEGACY = Pattern.compile("..."); // same grammar as ContentionStrategy.LEGACY
if (!LEGACY.matcher(cfgValue).matches()) throw new IllegalArgumentException("paxos contention wait string invalid: " + cfgValue);

try { LegacyWait w = LegacyWait.parseLegacy(value, ...); } catch (IllegalArgumentException e) { /* fix cassandra.yaml value, e.g. '1ms,10ms' */ }

When it happens

Trigger: Setting paxos contention wait configuration (paxos_contention_wait_random, _min, _max style legacy strings) to a value that doesn't match the LEGACY pattern — e.g. missing units, wrong separators, or garbage like 'foo' instead of '10ms' or '1ms,10ms'.

Common situations: Typo in cassandra.yaml contention settings; using new-format syntax against a legacy parser; missing time unit (e.g. '100' instead of '100ms'); whitespace or comma/semicolon mixups.

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

• CasWriteTimeoutException
• CasWriteTimeoutException
• Operation timed out
• WRITE_TIMEOUT
• Can't do any consensus migrations to/from PaxosV1, switch…

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/f6004974d4862c32. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/service/paxos/ContentionStrategy.java:298

    private static String orElse(Supplier<String> get, String orElse)
    {
        String result = get.get();
        return result != null ? result : orElse;
    }

    @VisibleForTesting
    static LegacyWait parseLegacy(String spec, boolean isMin)
    {
        long defaultMaxMicros = getRpcTimeout(MICROSECONDS);
        return parseLegacy(spec, 0, defaultMaxMicros, isMin ? 0 : defaultMaxMicros, LATENCIES);
    }

    public static LegacyWait parseLegacy(String input, long defaultMinMicros, long defaultMaxMicros, long onFailure, LatencySourceFactory latencies)
    {
        Matcher m = LEGACY.matcher(input);
        if (!m.matches())
            throw new IllegalArgumentException(input + " does not match " + LEGACY);

        String maybeConst = m.group("const");
        if (maybeConst != null)
        {
            long v = parseInMicros(maybeConst);
            return new LegacyWait(v, v, v, new Wait.Constant(v));
        }

        long min = parseInMicros(m.group("min"), defaultMinMicros);
        long max = parseInMicros(m.group("max"), defaultMaxMicros);
        return new LegacyWait(min, max, onFailure, TimeoutStrategy.parseWait(m.group("delegate"), latencies));
    }


    private static class LegacyWait implements Wait
    {
        final long min, max, onFailure;
        final Wait delegate;

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