MyCATApache/Mycat-Server · error · ConfigException

node name duplicated

Error message

node name duplicated :${name}

What it means

ClusterConfig.loadNode parses <node> elements from the Mycat cluster XML (cluster.xml). Each node must have a unique 'name' attribute; if a second element has the same name it throws ConfigException 'node name duplicated'. This prevents ambiguous node definitions in the cluster model.

Solutions

  1. Open cluster.xml and find all <node> elements sharing the same name attribute.
  2. Rename one node to a unique name (e.g. nodeM1, nodeM2) and update any <group nodeList=...> references to match.
  3. Search the file for 'node name=' and de-duplicate before restarting Mycat.
  4. If config is generated, fix the generator/template to enforce unique names.

Example fix

<!-- before -->
<node name="nodeM1" host="10.0.0.1" ... />
<node name="nodeM1" host="10.0.0.2" ... />
<!-- after -->
<node name="nodeM1" host="10.0.0.1" ... />
<node name="nodeM2" host="10.0.0.2" ... />
Defensive patterns

Strategy: validation

Validate before calling

// Before startup, check for duplicate node names in cluster.xml
import javax.xml.xpath.*;
var doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse("cluster.xml");
var nodes = XPathFactory.newInstance().newXPath().evaluate("//node/@name", doc, XPathConstants.NODESET);
var seen = new java.util.HashSet<String>();
for (int i = 0; i < nodes.getLength(); i++) {
  String n = nodes.item(i).getNodeValue().trim();
  if (!seen.add(n)) throw new IllegalStateException("duplicate node name: " + n);
}

Try / catch

try { new ClusterConfig(); } catch (ConfigException e) { if (e.getMessage().startsWith("node name duplicated")) { log.error("Fix duplicate <node name> in cluster.xml"); } throw e; }

Prevention

When it happens

Trigger: XML contains two or more <node name="X" ...> elements with the same trimmed name; thrown at ClusterConfig.java:73 while loadNode iterates the node list.

Common situations: Copy-paste of a <node> block when adding a second host without renaming it, merge conflicts in cluster.xml that duplicated a block, or automated config generation emitting duplicates.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/dcdfa346af7a80ad. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/config/model/ClusterConfig.java:73

    public Map<String, MycatNodeConfig> getNodes() {
        return nodes;
    }

    public Map<String, List<String>> getGroups() {
        return groups;
    }

    private static Map<String, MycatNodeConfig> loadNode(Element root, int port) {
        Map<String, MycatNodeConfig> nodes = new HashMap<String, MycatNodeConfig>();
        NodeList list = root.getElementsByTagName("node");
        Set<String> hostSet = new HashSet<String>();
        for (int i = 0, n = list.getLength(); i < n; i++) {
            Node node = list.item(i);
            if (node instanceof Element) {
                Element element = (Element) node;
                String name = element.getAttribute("name").trim();
                if (nodes.containsKey(name)) {
                    throw new ConfigException("node name duplicated :" + name);
                }

                Map<String, Object> props = ConfigUtil.loadElements(element);
                String host = (String) props.get("host");
                if (null == host || "".equals(host)) {
                    throw new ConfigException("host empty in node: " + name);
                }
                if (hostSet.contains(host)) {
                    throw new ConfigException("node host duplicated :" + host);
                }

                String wei = (String) props.get("weight");
                if (null == wei || "".equals(wei)) {
                    throw new ConfigException("weight should not be null in host:" + host);
                }
                int weight = Integer.parseInt(wei);
                if (weight <= 0) {
                    throw new ConfigException("weight should be > 0 in host:" + host + " weight:" + weight);

View on GitHub (pinned to 65f8d8beb7)