MyCATApache/Mycat-Server · critical · io.mycat.config.ConfigException

SelfCheck### there are some datasource connection failed…

Error message

SelfCheck### there are some datasource connection failed, pls check!

What it means

Thrown by ConfigInitializer.testConnection when at least one configured dataHost datasource failed its connectivity test during a full config reload (reload_all). The initializer probes each datasource connection and aggregates results; if any isConnectivity flag stays false it throws this ConfigException so the reload aborts with a broken backend rather than serving traffic through a dead datasource.

Solutions

  1. Check the MyCat log for the preceding 'test <name> database connection' failure lines to identify which datasource failed.
  2. Verify the failing backend MySQL is running: connect directly with mysql client using the dataHost user/password/host/port from schema.xml.
  3. Fix the root cause (start MySQL, correct host/port/credentials, open firewall/network path).
  4. Retry the reload (reload @@config_all) and confirm the self-check passes.
  5. Remove or correct the datasource definition if that backend is permanently decommissioned.

Example fix

// before (schema.xml)
<dataHost name="host1"><heartbeat>select user()</heartbeat>
  <writeHost host="m1" url="10.0.0.5:3306" user="root" password="old"/>
</dataHost>
// after (corrected credentials)
<dataHost name="host1"><heartbeat>select user()</heartbeat>
  <writeHost host="m1" url="10.0.0.5:3306" user="root" password="newpass"/>
</dataHost>
Defensive patterns

Strategy: try-catch

Validate before calling

// Probe each datasource before reload
for (String host : dataHosts.keySet()) {
    try (Connection c = DriverManager.getConnection(jdbcUrl, user, pass)) {
        // reachable
    } catch (SQLException e) {
        LOGGER.error("datasource {} unreachable: {}", host, e.getMessage());
    }
}

Try / catch

try {
    reloadAll();
} catch (ConfigException e) {
    if (e.getMessage().contains("datasource connection failed")) {
        LOGGER.error("Backend connectivity check failed; keeping current config: {}", e.getMessage());
        // alert ops, keep old config active
    } else { throw e; }
}

Prevention

When it happens

Trigger: Calling the reload (reload_all, e.g. via manager 'reload @@config_all') while one or more MySQL backends defined in schema.xml <dataHost> entries are unreachable — host down, wrong port, bad credentials, firewall, or MySQL not accepting connections.

Common situations: A backend MySQL instance stopped or crashed; failover environment where a standby host is offline; wrong IP/port/password after infrastructure changes; network/firewall or DNS changes blocking MyCat-to-MySQL traffic; check SQL/schema property misconfiguration.

Understand the failure class

Background: ECONNREFUSED and "connection refused" / "could not connect to server" errors: what they mean and how to fix them — this error's family across 44 libraries.

Related errors

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/fbc129533e7d332d. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/config/ConfigInitializer.java:214

				}
			}
			
			//
			boolean isConnectivity = true;
			for (Map.Entry<String, Boolean> entry : map.entrySet()) {
				String key = entry.getKey();
				Boolean value = entry.getValue();
				if ( !value && isConnectivity ) {
					LOGGER.warn("SelfCheck### test " + key + " database connection failed ");							
					isConnectivity = false;
					
				} else {
					LOGGER.info("SelfCheck### test " + key + " database connection success ");
				}
			}
			
			if ( !isConnectivity ) {
				throw new ConfigException("SelfCheck### there are some datasource connection failed, pls check!");
			}
				
		}
		
	}

	public SystemConfig getSystem() {
		return system;
	}

	public MycatCluster getCluster() {
		return cluster;
	}

	public FirewallConfig getFirewall() {
		return firewall;
	}

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