What causes "DC weights must be zero or positive" in apache/cassandra?

Replace the negative weight with 0 to effectively deprioritize that DC

apache/cassandra · error · ConfigurationException

DC weights must be zero or positive

Error message

DC weights must be zero or positive

What it means

WeightedDc.validateWeight parses the weight part of a dcs entry as an int and rejects negative values with a ConfigurationException ('DC weights must be zero or positive'). Weights determine how strongly a DC participates in Accord fast-path electorate selection; zero means least preferred.

Source

Thrown at src/java/org/apache/cassandra/service/accord/topology/ParameterizedFastPathStrategy.java:134

        public String toString()
        {
            return autoWeight ? name : name + ':' + weight;
        }

        static String validateDC(String dc)
        {
            dc = dc.trim();
            if (dc.isEmpty())
                throw cfe("dc name must not be empty", DCS);
            return dc;
        }

        static int validateWeight(String w)
        {
            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);
        }
    }

View on GitHub (pinned to 88fd0f6a0e)

Solutions

Replace the negative weight with 0 to effectively deprioritize that DC
Use positive integers to rank DCs, e.g. dcs=dc1:1,dc2:3
Re-issue the ALTER/CREATE keyspace statement with corrected weights

Example fix

// before
'dcs':'dc1:-2,dc2:5'

// after
'dcs':'dc1:0,dc2:5'

Defensive patterns

Strategy: validation

Validate before calling

for (String entry : dcs.split(",")) {
    String[] parts = entry.trim().split(":");
    if (parts.length == 2 && Integer.parseInt(parts[1]) < 0)
        throw new IllegalArgumentException("negative weight in dcs entry: " + entry);
}

Try / catch

try { applyFastPathOption(opts); } catch (org.apache.cassandra.exceptions.ConfigurationException e) {
    if (e.getMessage().contains("zero or positive"))
        log.error("Replace negative dc weights with 0 to deprioritize a DC");
}

Prevention

Use 0 (not negative) to deprioritize a DC
Compute weights with clamping: Math.max(0, w)
Document valid weight range (>= 0) wherever the option is exposed
Unit-test generated fast_path option maps for non-negative weights

When it happens

Trigger: Providing a dcs entry with a negative weight such as 'dcs=dc1:-1' or 'dc2:-5' when configuring a parameterized fast_path strategy.

Common situations: Typo'd minus sign where the operator intended to deprioritize a DC (should be weight 0); arithmetic applied to weights yielding negatives; editing serialized asMap output by hand.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/e037744040da3833. Report an issue: GitHub.