What causes "Missing separator " in apache/cassandra?

Use the exact separator the caller expects (e.g. write 4x2GB when 'x' is the separator)

apache/cassandra · error · NumberFormatException

Missing separator

Error message

Missing separator

What it means

parseHumanReadable supports values combining a number and a second component separated by a literal separator (e.g. '4x2GB' or '2 x 5GB'). This NumberFormatException is thrown when the expected separator string is not found at the position right after the parsed number.

Solutions

Use the exact separator the caller expects (e.g. write 4x2GB when 'x' is the separator)
Remove extra whitespace if the separator match is exact (e.g. use '4x2GB' not '4 x 2GB' when separator is 'x')
Check the calling code to see which separator string it passes and match it in your config
Make the separator optional in the caller if both forms should be accepted

Example fix

// before: parseHumanReadable("4*2GB", "x", "GB")
// after:  parseHumanReadable("4x2GB", "x", "GB")

Defensive patterns

Strategy: validation

Validate before calling

if (separator != null && !value.contains(separator)) throw new IllegalArgumentException("expected separator '" + separator + "' in " + value);

Try / catch

try { return FBUtilities.parseHumanReadable(s, "x", "GB"); } catch (NumberFormatException e) { throw new ConfigurationException("Value '" + s + "' must look like '4x2GB'", e); }

Prevention

Match the exact separator character the calling code expects
Document the accepted value format next to the config option
Normalize whitespace before parsing

When it happens

Trigger: Calling parseHumanReadable(datum, separator, unit) where datum contains a number+unit but lacks the required separator, e.g. parseHumanReadable("4x2GB", "x", "GB") given "4*2GB" or "4 2GB".

Common situations: Config values using a different separator character than the caller expects (asterisk vs 'x'), missing separator entirely, or extra whitespace preventing an exact match.

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

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/e204f2871e2531bd. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/utils/FBUtilities.java:1143

        double v = Double.parseDouble(m.group(0));

        int pos = m.end();
        if (m.group(2) == null) // possible binary exponent, parse
        {
            m = BINARY_EXPONENT.matcher(datum);
            m.region(pos, end);
            if (m.lookingAt())
            {
                int power = Integer.parseInt(m.group(1));
                v = Math.scalb(v, power);
                pos = m.end();
            }
        }

        if (separator != null)
        {
            if (!datum.startsWith(separator, pos))
                throw new NumberFormatException("Missing separator " + separator + " in " + datum);
            pos += separator.length();
        }
        else
        {
            while (pos < end && Character.isWhitespace(datum.charAt(pos)))
                ++pos;
        }

        if (pos < end)
        {
            char prefixChar = datum.charAt(pos);
            int prefixIndex = UNIT_PREFIXES.indexOf(prefixChar);
            if (prefixIndex >= 0)
            {
                prefixIndex -= UNIT_PREFIXES_BASE;
                ++pos;
                if (pos < end && datum.charAt(pos) == 'i')
                {

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