apache/cassandra · error · ConfigurationException

fast_path must be set to 'keyspace' or 'default' or a map…

Error message

fast_path must be set to 'keyspace' or 'default' or a map defining '%s' and optionally '%s'

What it means

ParameterizedFastPathStrategy.fromMap throws a ConfigurationException when the fast_path option is a map but lacks the required 'size' key. A map-valued fast_path must define 'size' and optionally 'dcs'; without 'size' the strategy cannot be constructed, and the message states the accepted forms ('keyspace', 'default', or such a map).

Solutions

1. Add the required size key with a positive integer, e.g. {fast_path: {'size':'4', 'dcs':'dc1:1'}}
2. Check for key spelling/case errors ('size' exactly)
3. If no parameterization is needed, use the string forms fast_path='keyspace' or fast_path='default' instead of a map

Example fix

// before
ALTER KEYSPACE ks WITH options = {fast_path: {'dcs':'dc1:1'}}

// after
ALTER KEYSPACE ks WITH options = {fast_path: {'size':'4', 'dcs':'dc1:1'}}

if (!map.containsKey("size"))
    throw new IllegalArgumentException("fast_path map requires 'size'; got keys: " + map.keySet());
Integer.parseInt(map.get("size")); // also fail fast on non-numeric size

try { applyFastPathOption(opts); } catch (org.apache.cassandra.exceptions.ConfigurationException e) {
    if (e.getMessage().contains("fast_path must be set"))
        log.error("Map-valued fast_path must define 'size' (and optionally 'dcs')");
}

When it happens

Trigger: Setting a keyspace/table fast_path option to a map that contains only 'dcs' (or other keys) without 'size', e.g. {fast_path: {'dcs':'dc1'}}.

Common situations: Typo'd key ('sizes', 'Size') instead of 'size'; operator assuming dcs alone suffices; copying a partial example; camelCasing when serializing options through a tool that alters keys.

Understand the failure class

Background: "is required", "must be set", "missing required field": configuration validation errors across open-source libraries — this error's family across 36 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/bc105a67cc30647a. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/service/accord/topology/ParameterizedFastPathStrategy.java:244

        Node.Id[] array = new Node.Id[fpSize];
        for (int i=0; i<fpSize; i++)
            array[i] = sorters.get(i).id;

        Arrays.sort(array);
        SortedArrayList<Node.Id> electorate = new SortedArrayList<>(array);
        Invariants.require(electorate.size() >= slowQuorum);
        return electorate;
    }

    private static ConfigurationException cfe(String fmt, Object... args)
    {
        return new ConfigurationException(String.format(fmt, args));
    }

    public static ParameterizedFastPathStrategy fromMap(Map<String, String> map)
    {
        if (!map.containsKey(SIZE))
            throw cfe("fast_path must be set to 'keyspace' or 'default' or a map defining '%s' and optionally '%s'", SIZE, DCS);

        int size;
        try
        {
            size = Integer.parseInt(map.get(SIZE));
        }
        catch (NumberFormatException e)
        {
            throw cfe("%s must be a positive number, got %s", SIZE, map.get(SIZE));
        }

        if (size < 1)
            throw cfe("%s must be greater than zero", SIZE);

        ImmutableMap<String, WeightedDc> dcMap;
        if (map.containsKey(DCS) && !map.get(DCS).isEmpty())
        {
            Map<String, WeightedDc> mutableDcs = new HashMap<>();

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