MyCATApache/Mycat-Server · error · RuntimeException

offer data error!

Error message

offer data error!

What it means

MySQLConnectionHandler (a NIO packet handler) queues incoming backend packets onto the connection's processor executor via offerData(). If the queue rejects the task (executor queue full/shutdown), offerDataError() is invoked, which resets resultStatus to RESULT_STATUS_INIT and throws RuntimeException("offer data error!").

Solutions

1. Increase the processor's task queue size / NIO processor count in server.xml (processors, processorExecutorSize) to absorb bursts
2. Investigate and fix the slow consumer (responseHandler) that lets the queue fill — often a stuck frontend session or slow SQL
3. Add/keep rejection handling so the backend connection is closed cleanly instead of an uncaught RuntimeException propagating through the NIO thread
4. Retry the query; this is transient under load

try { session.execute(...); } catch (RuntimeException e) { if ("offer data error!".equals(e.getMessage())) { session.close(); /* retry on a new connection */ } else { throw e; } }

When it happens

Trigger: The backend connection's processor executor queue is full or its executor has been shut down while binary/row packets arrive, so offerData(data, source.getProcessor().getExecutor()) cannot enqueue the packet.

Common situations: Heavy load with a saturated NIO processor queue (QueueSize limit hit), system overload or executor rejection policy discarding tasks, backend threads shutting down during MyCat shutdown while connections still stream data.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• offer data error!
• unknown status!
• global seq and share join and special…
• txIsolation
• err.errno

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/34eda6e8efe2844b. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/backend/mysql/nio/MySQLConnectionHandler.java:91

		if (responseHandler != null) {
			responseHandler.connectionError(e, source);
		}
		LOGGER.error("connectionError but not handle");
	}

	public MySQLConnection getSource() {
		return source;
	}

	@Override
	public void handle(byte[] data) {
		offerData(data, source.getProcessor().getExecutor());
	}

	@Override
	protected void offerDataError() {
		resultStatus = RESULT_STATUS_INIT;
		throw new RuntimeException("offer data error!");
	}

	@Override
	protected void handleData(byte[] data) {
		switch (resultStatus) {
			case RESULT_STATUS_INIT:
				switch (data[4]) {
					case OkPacket.FIELD_COUNT:
                        int packetSize = (int) ByteUtil.readLength(data, 0);
                        // COM_STMT_PREPARE_OK状态标识 [00]，和OK包一致，区别是COM_STMT_PREPARE_OK固定长度为12
                        if (packetSize == PreparedOkPacket.PACKET_SIZE
                                && (responseHandler != null && responseHandler instanceof PrepareRequestHandler)) {
                            handlePrepareOkPacket(data);
                            resultStatus = RESULT_STATUS_PREPARE_RESPONSE_OK;
                        } else {
                            handleOkPacket(data);
                        }
						break;

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