vitessio/vitess · error

FindReplicas: malformed addr %v

Error message

FindReplicas: malformed addr %v

What it means

FindReplicas parses the replica host addresses reported by `SHOW SLAVE STATUS`/processlist. Each address is passed to netutil.SplitHostPort, and if the address cannot be split into host and port, this error is thrown, aborting the whole lookup.

Source

Thrown at go/vt/mysqlctl/replication.go:1159

	qr, err := mysqld.FetchSuperQuery(ctx, "SHOW PROCESSLIST")
	if err != nil {
		return nil, err
	}
	addrs := make([]string, 0, 32)
	for _, row := range qr.Rows {
		// Check for prefix, since it could be "Binlog Dump GTID".
		if strings.HasPrefix(row[colCommand].ToString(), binlogDumpCommand) {
			host := row[colClientAddr].ToString()
			if host == "localhost" {
				// If we have a local binlog streamer, it will
				// show up as being connected
				// from 'localhost' through the local
				// socket. Ignore it.
				continue
			}
			host, _, err = netutil.SplitHostPort(host)
			if err != nil {
				return nil, fmt.Errorf("FindReplicas: malformed addr %v", err)
			}
			var ips []string
			ips, err = net.LookupHost(host)
			if err != nil {
				return nil, fmt.Errorf("FindReplicas: LookupHost failed %v", err)
			}
			addrs = append(addrs, ips...)
		}
	}

	return addrs, nil
}

// GetGTIDMode gets the GTID mode for the server
func (mysqld *Mysqld) GetGTIDMode(ctx context.Context) (string, error) {
	conn, err := getPoolReconnect(ctx, mysqld.dbaPool)
	if err != nil {
		return "", err

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Check the replication topology output (`SHOW REPLICAS` / `SHOW SLAVE STATUS`) for malformed or missing addr values
2. Fix the replica's report_host/report_port configuration so it reports a valid host:port
3. Ensure replicas connect over TCP with a proper port rather than a local socket
4. Re-run FindReplicas after correcting the replication configuration

Example fix

// before: replica reporting via unix socket
// after: in replica my.cnf
// report_host = 10.0.0.5
// report_port = 3306

// validate replica addrs before calling FindReplicas
for _, a := range replicaAddrsFromStatus {
    if _, _, err := netutil.SplitHostPort(a); err != nil {
        log.Warnf("skipping malformed replica addr %q", a)
    }
}

addrs, err := mysqld.FindReplicas()
if err != nil && strings.Contains(err.Error(), "malformed addr") {
    log.Warn("replica reported malformed addr; check report_host config", slog.Any("error", err))
}

When it happens

Trigger: Calling FindReplicas (directly or via GetReplicas) when a replica reports an addr that is not a valid host:port pair — e.g. empty or malformed host in SHOW REPLICAS / SHOW SLAVE STATUS output.

Common situations: Replica connected over a unix socket or reporting 'localhost' variants that escape the earlier localhost filter; unusual replication setups or network configurations where the reported addr lacks a port.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• FindReplicas: LookupHost failed %v
• failed to set @source_binlog_checksum=@@global.binlog_checks
• failed to send the ComBinlogDump command: %v
• can't dial mysqlctld: %v
• invalid key:value pair

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/aa40b8b0f8241d66. Report an issue: GitHub.