MyCATApache/Mycat-Server · error · RuntimeException

errr

Error message

 errr

What it means

In the close(reason) path, AbstractConnection detects that the close reason string itself contains 'connection,reason:java.net.ConnectException' — i.e. a nested/recursive close with a ConnectException reason — and throws RuntimeException(" errr") as a debug guard. It indicates the connection is being closed because a backend connect failed.

Solutions

1. Fix backend connectivity: verify dataHost url host/port, that MySQL is running, and reachable (telnet/nc the port).
2. Correct schema.xml dataNode/dataHost configuration and reload config.
3. Check firewalls/security groups between mycat and the MySQL nodes.
4. If this is a cascaded close (double close), fix the caller that closes twice; upgrade mycat where double-close cleanup was fixed (e.g. issue#1616 style fixes).

Example fix

// before (schema.xml)
<writeHost host="hostM1" url="10.0.0.3:3307" .../>
// after
<writeHost host="hostM1" url="10.0.0.3:3306" .../>

// probe backend before routing requests
try (Socket s = new Socket()) {
    s.connect(new InetSocketAddress(host, port), 3000); // must succeed
}

try {
    conn.close(reason);
} catch (RuntimeException e) {
    if (" errr".equals(e.getMessage())) {
        LOGGER.error("backend connect failed; verify dataHost {}:{}", host, port);
    }
}

When it happens

Trigger: close(String reason) is invoked with a reason produced by a previous failed close containing 'java.net.ConnectException', typically when mycat cannot establish a TCP connection to a backend MySQL node.

Common situations: Backend MySQL down or wrong host/port in schema.xml/dataHost config; firewall blocking the port; DNS failure; backend pool exhausted and connect refused during failover.

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

• failed to connect to zookeeper service
• Unexpected exception
• err.errno
• Unknown Packet!
• SelfCheck### there are some datasource connection failed…

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/06b0f665e08c40aa. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/net/AbstractConnection.java:533

	@Override
	public void close(String reason) {
		if (!isClosed.get()) {
			closeSocket();
			isClosed.set(true);
			if (processor != null) {
				processor.removeConnection(this);
			}
			this.cleanup();
			isSupportCompress = false;

			// ignore null information
			if (Strings.isNullOrEmpty(reason)) {
				return;
			}
			LOGGER.info("close connection,reason:" + reason + " ," + this);
			if (reason.contains("connection,reason:java.net.ConnectException")) {
				throw new RuntimeException(" errr");
			}
		} else {
		    // make sure cleanup again
		    // Fix issue#1616
		    this.cleanup();
		}
	}

	public boolean isClosed() {
		return isClosed.get();
	}

	public void idleCheck() {
		if (isIdleTimeout()) {
			LOGGER.info(toString() + " idle timeout");
			close(" idle ");
		}
	}

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