apache/cassandra · error · ConfigurationException

Invalid dc weighting syntax

Error message

Invalid dc weighting syntax %s, use <dc>:<weight>

What it means

WeightedDc.fromString throws a ConfigurationException when a dcs entry splits on the colon separator into more than two parts, i.e. it is not of the form <dc> or <dc>:<weight>. The message shows the offending entry and the required '<dc>:<weight>' syntax.

Solutions

1. Rewrite each entry as either '<dc>' or '<dc>:<weight>' with exactly one colon at most
2. Rename the datacenter to avoid colons, or reference it via a colon-free alias
3. Validate the list with a regex like ^[^:]+(:\d+)?$ per entry before applying

Example fix

// before
'dcs':'dc1:1:2,dc2'

// after
'dcs':'dc1:1,dc2'

java.util.regex.Pattern OK = java.util.regex.Pattern.compile("^[^:]+(:\\d+)?$");
for (String entry : dcs.split(",")) {
    if (!OK.matcher(entry.trim()).matches())
        throw new IllegalArgumentException("entry must be <dc> or <dc>:<weight>: " + entry);
}

try { applyFastPathOption(opts); } catch (org.apache.cassandra.exceptions.ConfigurationException e) {
    if (e.getMessage().contains("use <dc>:<weight>"))
        log.error("Each dcs entry may contain at most one colon separating dc and weight");
}

When it happens

Trigger: Passing a dcs entry containing multiple colons such as 'dc1:1:2' or a DC name that itself contains a colon (e.g. an IPv6-ish or namespaced name) to the accord parameterized fast_path strategy.

Common situations: Operators pasting composite identifiers with colons; accidental double-colon (e.g. 'dc1::2'); confusion with other weight syntaxes (yaml maps) elsewhere in Cassandra config.

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

• accord.cache_size option was set incorrectly to
• accord.journal_directory must not be the same as any…
• Cannot change transactional mode to
• dc name must not be empty
• DC weights must be zero or positive

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/8aa86173ae6125d3. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/service/accord/topology/ParameterizedFastPathStrategy.java:150

            int weight = Integer.parseInt(w);
            if (weight < 0)
                throw cfe("DC weights must be zero or positive");
            return weight;
        }

        static WeightedDc fromString(String s, int idx)
        {
            s = s.trim();
            if (s.isEmpty())
                throw cfe("%s entries must not be empty", DCS);

            String[] parts = COLON_SEPARATOR.split(s);
            if (parts.length == 1)
                return new WeightedDc(validateDC(parts[0]), idx, true);
            else if (parts.length == 2)
                return new WeightedDc(validateDC(parts[0]), validateWeight(parts[1]), false);
            else
                throw cfe("Invalid dc weighting syntax %s, use <dc>:<weight>", s);
        }
    }

    public final int size;
    private final ImmutableMap<String, WeightedDc> dcs;

    ParameterizedFastPathStrategy(int size, ImmutableMap<String, WeightedDc> dcs)
    {
        this.size = size;
        this.dcs = dcs;
    }

    public boolean equals(Object o)
    {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ParameterizedFastPathStrategy that = (ParameterizedFastPathStrategy) o;
        return size == that.size && Objects.equals(dcs, that.dcs);

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