apache/beam · error

node %v is reachable by edge %v, but it's not in same graph

Error message

node %v is reachable by edge %v, but it's not in same graph

What it means

Graph.Build() keeps a map of nodes reachable via edges and verifies each reachable node exists in the current graph's node set. When an edge points to a node that was created in (or attributed to) a different Graph, Build returns "node %v is reachable by edge %v, but it's not in same graph" — a graph-identity invariant violation.

Source

Thrown at sdks/go/pkg/beam/core/graph/graph.go:111

	}
	// Build a map of all nodes that are reachable by g.edges.
	reachable := make(map[*Node]*MultiEdge)
	for _, e := range g.edges {
		for _, i := range e.Input {
			reachable[i.From] = e
		}
		for _, o := range e.Output {
			reachable[o.To] = e
		}
	}
	for n := range nodes {
		if _, ok := reachable[n]; !ok {
			return nil, nil, errors.Errorf("node %v in graph is unconnected", n.id)
		}
	}
	for n, e := range reachable {
		if _, ok := nodes[n]; !ok {
			return nil, nil, errors.Errorf("node %v is reachable by edge %v, but it's not in same graph", n.id, e.id)
		}
	}
	return g.edges, g.nodes, nil
}

func (g *Graph) String() string {
	var nodes []string
	for _, node := range g.nodes {
		nodes = append(nodes, node.String())
	}
	var edges []string
	for _, edge := range g.edges {
		edges = append(edges, edge.String())
	}
	return fmt.Sprintf("Nodes: %v\nEdges: %v", strings.Join(nodes, "\n"), strings.Join(edges, "\n"))
}

View on GitHub (pinned to 12126d8942)

Solutions

1. Ensure every node referenced by an edge was created with the same Graph instance (same g.NewNode call chain).
2. Don't reuse PCollection/node values across pipeline or graph scopes; recreate them in the new graph.
3. Refactor custom transforms to receive the Graph from a single owner instead of constructing their own.
4. If hit via normal beam.Pipeline usage, this indicates an SDK bug — report with a minimal repro and pin/upgrade Beam version.

When it happens

Trigger: Building a Graph where an edge's Output.To (or Input.From) node was created by another Graph instance, e.g. mixing nodes across two g := graph.New() scopes or reusing nodes from a previous pipeline in a new one.

Common situations: Low-level custom transform code that creates nodes with one graph but edges with another; sharing PCollections/nodes between pipelines; copy-pasted graph-construction code using stale variables.

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

• node %v in graph is unconnected
• too few params
• too few inputs: forgot an input or to annotate options?
• too many inputs
• needs at least 1 input

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/2a2953b08853a11a. Report an issue: GitHub.