apache/dolphinscheduler · error · IllegalArgumentException

"The task " + taskDefinition + " is already exists"

Error message

"The task " + taskDefinition + " is already exists"

What it means

addTaskNodes initializes the predecessor/successor adjacency lists for every task name in the graph. If a task name already has an entry, the task is being added twice and the graph would be corrupt, so it throws this IllegalArgumentException.

Source

Thrown at dolphinscheduler-master/src/main/java/org/apache/dolphinscheduler/server/master/engine/graph/WorkflowGraph.java:115

        TaskDefinition taskDefinition = taskDefinitionCodeMap.get(taskCode);
        if (taskDefinition == null) {
            throw new IllegalArgumentException("Cannot find task: " + taskCode);
        }
        return taskDefinition;
    }

    @Override
    public List<TaskDefinition> getAllTaskNodes() {
        return new ArrayList<>(taskDefinitionMap.values());
    }

    private void addTaskNodes(List<TaskDefinition> taskDefinitions) {
        taskDefinitions
                .stream()
                .map(TaskDefinition::getName)
                .forEach(taskDefinition -> {
                    if (predecessors.containsKey(taskDefinition) || successors.containsKey(taskDefinition)) {
                        throw new IllegalArgumentException("The task " + taskDefinition + " is already exists");
                    }
                    predecessors.put(taskDefinition, new ArrayList<>());
                    successors.put(taskDefinition, new ArrayList<>());
                });
    }

    private void addTaskEdge(List<WorkflowTaskRelation> workflowTaskRelations) {
        for (WorkflowTaskRelation workflowTaskRelation : workflowTaskRelations) {
            long pre = workflowTaskRelation.getPreTaskCode();
            long post = workflowTaskRelation.getPostTaskCode();
            if (pre > 0 && post > 0) {

                if (!taskDefinitionCodeMap.containsKey(pre)) {
                    throw new IllegalArgumentException("Cannot find task: " + pre);
                }
                if (!taskDefinitionCodeMap.containsKey(post)) {
                    throw new IllegalArgumentException("Cannot find task: " + post);
                }

View on GitHub (pinned to 02eac45a1b)

Solutions

1. Ensure task names are unique across the workflow's task definitions before constructing the graph
2. Deduplicate the input list by name (or fix upstream so duplicate definitions are not produced)
3. If intentionally re-adding tasks, clear or rebuild the WorkflowGraph instead of mutating it
4. Check the workflow definition in t_ds_task_definition for duplicate name rows

Example fix

// before
List<TaskDefinition> tasks = loadTasks(); // may contain duplicates
WorkflowGraph g = new WorkflowGraph(tasks, relations);
// after
List<TaskDefinition> unique = tasks.stream()
        .collect(Collectors.toMap(TaskDefinition::getName, t -> t, (a, b) -> a))
        .values().stream().collect(Collectors.toList());
WorkflowGraph g = new WorkflowGraph(unique, relations);

Set<String> names = new HashSet<>();
for (TaskDefinition t : taskDefinitions) {
    if (!names.add(t.getName())) throw new IllegalStateException("Duplicate task name: " + t.getName());
}

try {
    WorkflowGraph graph = new WorkflowGraph(taskDefinitions, relations);
} catch (IllegalArgumentException e) {
    if (e.getMessage().contains("is already exists")) log.error("Duplicate task in graph: {}", e.getMessage());
    throw e;
}

When it happens

Trigger: Constructing a WorkflowGraph whose List<TaskDefinition> contains two definitions with the same name (streamed through TaskDefinition::getName). Internally this is reachable after the duplicate-code/name checks at lines 51-58 only if distinct names are impossible — in practice it fires on duplicate-name inputs when the earlier name check was bypassed (e.g. differing codes but the same name reaching addTaskNodes via different call paths).

Common situations: Duplicated task definitions with different codes but identical names in the workflow definition list; calling an overloaded constructor or add path twice with overlapping task lists; hand-built graphs in tests adding the same task twice.

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

• "Duplicate task code: " + taskDefinition.getCode() + " in th
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• data: %s should be a validate data string - yyyy-MM-dd HH:mm
• The date must not be null

AI-assisted analysis of apache/dolphinscheduler@02eac45a1b (2026-09-06). Data as JSON: /api/errors/3706bb27b85d3291. Report an issue: GitHub.