nathanmarz/storm · error · RuntimeException

Cannot have one group have fixed parallelism of two…

Error message

Cannot have one group have fixed parallelism of two different values

What it means

getFixedParallelism derives a group's fixed parallelism from the requiredNumPartitions of state specs in its nodes. If two different states in the same group require different partition counts, a single parallelism cannot satisfy both, so this RuntimeException is thrown during build.

Solutions

Set explicit, equal requiredNumPartitions on all state specs in the group
Add explicit parallelismHints and reorder/partition so the states are not in the same equivalence group
Give each state its own branch partitioned independently instead of sharing a group

Example fix

// before
HBaseState.Options o1 = new HBaseState.Options().setNumPartitions(4);
HBaseState.Options o2 = new HBaseState.Options().setNumPartitions(8); // same group
// after
HBaseState.Options o2 = new HBaseState.Options().setNumPartitions(4); // match required partitions

Defensive patterns

Strategy: validation

Validate before calling

// all states in a shared group must declare the same requiredNumPartitions
Set<Integer> reqs = states.stream().map(s -> s.getRequiredNumPartitions()).collect(Collectors.toSet());
if (reqs.size() > 1) throw new IllegalArgumentException("All co-grouped states must require the same partitions: " + reqs);

Try / catch

try {
    topology.build();
} catch (RuntimeException e) {
    if (e.getMessage().contains("fixed parallelism of two different values")) {
        throw new IllegalStateException("Unify requiredNumPartitions across states in the same group", e);
    } throw e;
}

Prevention

Use one shared constant for requiredNumPartitions across state specs
Partition states into separate branches when partition requirements differ
Build the topology in tests to surface the conflict pre-deploy

When it happens

Trigger: A TridentTopology with multiple persistentAggregates/states (e.g. two HBase or Redis map states with different requiredNumPartitions) whose nodes fall into the same parallelism-equivalence group.

Common situations: Several persistentAggregates downstream of a shared partitionBy/groupBy without explicit parallelismHints; migrating one state backend and adding a second with different partition requirements; merging two topology fragments into one TridentTopology.

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 nathanmarz/storm@cdb116e942 (2026-09-12). Data as JSON: /api/errors/0aa6328eb7c870ea. Report an issue: GitHub.

Appendix: source

Thrown at storm-core/src/jvm/storm/trident/TridentTopology.java:655

    
    private static Map getSpoutComponentConfig(Object spout) {
        if(spout instanceof IRichSpout) {
            return ((IRichSpout) spout).getComponentConfiguration();
        } else if (spout instanceof IBatchSpout) {
            return ((IBatchSpout) spout).getComponentConfiguration();
        } else {
            return ((ITridentSpout) spout).getComponentConfiguration();
        }
    }
    
    private static Integer getFixedParallelism(Set<Group> groups) {
        Integer ret = null;
        for(Group g: groups) {
            for(Node n: g.nodes) {
                if(n.stateInfo != null && n.stateInfo.spec.requiredNumPartitions!=null) {
                    int reqPartitions = n.stateInfo.spec.requiredNumPartitions;
                    if(ret!=null && ret!=reqPartitions) {
                        throw new RuntimeException("Cannot have one group have fixed parallelism of two different values");
                    }
                    ret = reqPartitions;
                }
            }
        }
        return ret;
    }
    
    private static boolean isIdentityPartition(PartitionNode n) {
        Grouping g = n.thriftGrouping;
        if(g.is_set_custom_serialized()) {
            CustomStreamGrouping csg = (CustomStreamGrouping) Utils.deserialize(g.get_custom_serialized());
            return csg instanceof IdentityGrouping;
        }
        return false;
    }
    
    private static void addEdge(DirectedGraph g, Object source, Object target, int index) {

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