MyCATApache/Mycat-Server · error · ConfigException

old config for migrate read fail!please check schema.xml or…

Error message

 old config for migrate read fail!please check schema.xml or  rule.xml  {e}

What it means

ConfigComparer.loadOldConfig loads the pre-migration sharding configuration using XMLSchemaLoader over the default schema.xml/rule.xml. Any parsing or validation failure in those XML files is wrapped as ConfigException(' old config for migrate read fail!please check schema.xml or rule.xml <cause>').

Solutions

Open the wrapped cause in the message — it names the actual XML parse or validation failure
Validate schema.xml and rule.xml are present in the expected location and well-formed XML (xmllint)
Ensure every <table> rule reference exists in rule.xml and all dataNode/dataHost names resolve
Run the migration with a config known to work: start Mycat normally first to confirm the old config loads

Example fix

// before
<!-- rule.xml missing rule="mod-rule" referenced by schema.xml -->
// after
add <tableRule name="mod-rule"> ... </tableRule> to rule.xml

Defensive patterns

Strategy: validation

Validate before calling

static boolean oldConfigReadable(String schemaXml, String ruleXml){
    try {
        javax.xml.parsers.DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new java.io.File(schemaXml));
        javax.xml.parsers.DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new java.io.File(ruleXml));
        return true;
    } catch (Exception e) { return false; }
}

Try / catch

try { comparer.loadOldConfig(); }
catch (ConfigException e) { LOG.error("old schema.xml/rule.xml unreadable: " + e.getMessage(), e); throw e; }

Prevention

Lint schema.xml and rule.xml (xmllint) before running migration
Verify every referenced rule/dataNode/dataHost exists in the pair of files
Keep old configs in version control so migrations use known-good copies
Boot Mycat with the same config first to prove it loads

When it happens

Trigger: Running the dataMigrator flow (MigrateRunner/ConfigComparer) when schema.xml or rule.xml is missing, malformed XML, references nonexistent dataHost/dataNode, or violates Mycat's schema rules.

Common situations: Old cluster configs copied incompletely to the migration working directory; hand-edited XML with unbalanced tags; DTD/xsd references broken; table/rule names mismatched between schema.xml and rule.xml.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/35a175a0f1e4e513. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/util/dataMigrator/ConfigComparer.java:83

	public ConfigComparer(boolean isAwaysUseMaster) throws Exception{
		this.isAwaysUseMaster = isAwaysUseMaster;
		loadOldConfig();
		loadNewConfig();
		loadTablesFile();
	}
	
	public List<TableMigrateInfo> getMigratorTables(){
		return migratorTables;
	}
	
	private void loadOldConfig(){
		try{
			oldLoader = new XMLSchemaLoader();
			oldDataHosts = oldLoader.getDataHosts();
			oldDataNodes = oldLoader.getDataNodes();
			oldSchemas = oldLoader.getSchemas();
		}catch(Exception e){
			throw new ConfigException(" old config for migrate read fail!please check schema.xml or  rule.xml  "+e);
		}
		
	}
	
	private void loadNewConfig(){
		try{
			newLoader = new XMLSchemaLoader(NEW_SCHEMA, NEW_RULE);
			newDataHosts = newLoader.getDataHosts();
			newDataNodes = newLoader.getDataNodes();
			newSchemas = newLoader.getSchemas();
		}catch(Exception e){
			throw new ConfigException(" new config for migrate read fail!please check newSchema.xml or  newRule.xml  "+e);
		}
		
	}
	
	
	private void loadTablesFile() throws Exception{

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