apache/cassandra · critical · IllegalArgumentException

cannot have two verbs that map to the same id: + v + and +…

Error message

cannot have two verbs that map to the same id: + v + and + idMap[v.id]

What it means

While building the verb-id lookup table at class-init, each NORMAL verb must map to a unique id. If a verb's id is already occupied by another verb in idMap, the registry would be ambiguous, so IllegalArgumentException is thrown.

Solutions

Find the two verbs named in the message and give one a fresh unique id.
Regenerate/renumber verb ids for any locally added MAPPING entries.
After a merge, compile and run the node once in a test env to exercise Verb class-init before deploy.

Example fix

// before
MAPPING(42, .., "PREPARE_MSG")
MAPPING(42, .., "COMMIT_MSG")
// after
MAPPING(42, .., "PREPARE_MSG")
MAPPING(43, .., "COMMIT_MSG")

Defensive patterns

Strategy: validation

Validate before calling

// test: assert all NORMAL verb ids unique
Set<Integer> ids = new HashSet<>();
for (Verb v : Verb.values()) if (v.kind == Kind.NORMAL) assertTrue(ids.add(v.id));

Prevention

Never hand-pick verb ids; allocate sequentially from a single owner
Add a CI test iterating all verbs for id uniqueness
Resolve Verb.java merge conflicts by renumbering, not by keeping both sides

When it happens

Trigger: Declaring two NORMAL Verbs with the same enum-assigned id (copy-paste of a MAPPING line without changing the id), then loading the Verb class.

Common situations: Merge conflicts in Verb.java that keep duplicate id literals; hand-edited patches adding new message types; rebase across versions where ids were renumbered.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/37d9fe3789d8dcf7. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/net/Verb.java:628

                default:
                    throw new AssertionError("Unsupported Verb Kind: " + v.kind + " for verb " + v);
            }
        }
        minCustomId = minCustom;

        if (minCustom <= max)
            throw new IllegalStateException("Overlapping verb ids are not allowed");

        Verb[] idMap = new Verb[max + 1];
        int customCount = minCustom < Integer.MAX_VALUE ? CUSTOM_VERB_START - minCustom : 0;
        Verb[] customIdMap = new Verb[customCount + 1];
        for (Verb v : verbs)
        {
            switch (v.kind)
            {
                case NORMAL:
                    if (idMap[v.id] != null)
                        throw new IllegalArgumentException("cannot have two verbs that map to the same id: " + v + " and " + idMap[v.id]);
                    idMap[v.id] = v;
                    break;
                case CUSTOM:
                    int relativeId = idForCustomVerb(v.id);
                    if (customIdMap[relativeId] != null)
                        throw new IllegalArgumentException("cannot have two custom verbs that map to the same id: " + v + " and " + customIdMap[relativeId]);
                    customIdMap[relativeId] = v;
                    break;
                default:
                    throw new AssertionError("Unsupported Verb Kind: " + v.kind + " for verb " + v);
            }
        }

        idToVerbMap = idMap;
        idToCustomVerbMap = customIdMap;
    }

    public static Verb fromId(int id)

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