MyCATApache/Mycat-Server · error · ConfigException

rule function duplicated!

Error message

rule function ${name} duplicated!

What it means

loadFunctions iterates <function> elements in rule.xml and stores them by name in a map. If two <function> blocks share the same name attribute, the second is rejected with this ConfigException. Duplicate function names would make algorithm lookup ambiguous.

Solutions

1. Search rule.xml for repeated <function name="..."> names; delete or rename the duplicate.
2. If you need the same algorithm with different parameters, create uniquely named functions and reference them from the corresponding tableRules.
3. Restart/reload and verify MyCat starts cleanly.

Example fix

// before (rule.xml)
<function name="mod-long" class="io.mycat.route.function.PartitionByMod">
  <property name="count">4</property>
</function>
<function name="mod-long" class="io.mycat.route.function.PartitionByMod">
  <property name="count">8</property>
</function>
// after
<function name="mod-long-4" class="io.mycat.route.function.PartitionByMod">
  <property name="count">4</property>
</function>
<function name="mod-long-8" class="io.mycat.route.function.PartitionByMod">
  <property name="count">8</property>
</function>

// Detect duplicate <function> names before deployment
Set<String> seen = new HashSet<>();
NodeList fns = doc.getElementsByTagName("function");
for (int i = 0; i < fns.getLength(); i++) {
    String name = ((Element) fns.item(i)).getAttribute("name");
    if (!seen.add(name)) throw new IllegalStateException("duplicate function: " + name);
}

try {
    ruleLoader.load();
} catch (ConfigException e) {
    if (e.getMessage().startsWith("rule function") && e.getMessage().contains("duplicated!")) {
        LOG.error("Duplicate <function> name in rule.xml: {}", e.getMessage());
    }
    throw e;
}

When it happens

Trigger: rule.xml defines two <function name="X" ...> elements with identical names, possibly with different class attributes; load() -> loadFunctions() hits functions.containsKey(name).

Common situations: Appending a new function definition without removing the old one during tuning (e.g. changing count); merging rule.xml from two environments; copy-paste duplication.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

• table rule duplicated!
• only one rule can defined
• can't find function of name
• table rule coulmns has multi values
• schema duplicated!

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/a4130c4eaaea2433. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/config/loader/xml/XMLRuleLoader.java:199

	 * @param root
	 * @throws ClassNotFoundException
	 * @throws InstantiationException
	 * @throws IllegalAccessException
	 * @throws InvocationTargetException
     */
	private void loadFunctions(Element root) throws ClassNotFoundException,
			InstantiationException, IllegalAccessException,
			InvocationTargetException {
		NodeList list = root.getElementsByTagName("function");
		for (int i = 0, n = list.getLength(); i < n; ++i) {
			Node node = list.item(i);
			if (node instanceof Element) {
				Element e = (Element) node;
				//获取name标签
				String name = e.getAttribute("name");
				//如果Map已有，则function重复
				if (functions.containsKey(name)) {
					throw new ConfigException("rule function " + name
							+ " duplicated!");
				}
				//获取class标签
				String clazz = e.getAttribute("class");
				//根据class利用反射新建分片算法
				AbstractPartitionAlgorithm function = createFunction(name, clazz);
				//根据读取参数配置分片算法
				ParameterMapping.mapping(function, ConfigUtil.loadElements(e));
				//每个AbstractPartitionAlgorithm可能会实现init来初始化
				function.init();
				//放入functions map
				functions.put(name, function);
			}
		}
	}

	private AbstractPartitionAlgorithm createFunction(String name, String clazz)
			throws ClassNotFoundException, InstantiationException,

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