MyCATApache/Mycat-Server · error · UnknownTxIsolationException

txIsolation

Error message

txIsolation:${txIsolation}

What it means

PostgreSQLBackendConnection.getTxIsolationCommand() builds a 'SET SESSION TRANSACTION ISOLATION LEVEL ...' command from the configured txIsolation value. Only READ_UNCOMMITTED/READ_COMMITTED/REPEATABLE_READ/SERIALIZABLE are mapped; any other integer (including PG-specific constants outside the Isolations table) hits the default branch and throws UnknownTxIsolationException("txIsolation:" + txIsolation).

Solutions

1. Set transactionIsolation to a supported value (1=READ_UNCOMMITTED, 2=READ_COMMITTED, 4=REPEATABLE_READ, 8=SERIALIZABLE) in the dataHost config
2. Log/capture the offending txIsolation value from the exception message and correct the caller that set it
3. Upgrade/patch MyCat to map PostgreSQL's own isolation constants in getTxIsolationCommand
4. If you need READ COMMITTED behavior, use isolation 2 rather than driver-specific values

Example fix

// before
<dataHost ... transactionIsolation="3">
// after
<dataHost ... transactionIsolation="2">

int tx = getTxIsolation();
if (tx != 1 && tx != 2 && tx != 4 && tx != 8) {
    throw new IllegalArgumentException("txIsolation " + tx + " unsupported by PG backend; use 1/2/4/8");
}

try { conn.execute(sql); } catch (UnknownTxIsolationException e) { /* correct transactionIsolation config from e.getMessage() and retry */ }

When it happens

Trigger: A backend connection is created/used with a txIsolation value that is not one of the four supported Isolations constants — typically a bad value in the transactionIsolation config, or a caller passing a JDBC constant MyCat's Isolations table does not recognize.

Common situations: Typo'd or out-of-range isolation level in the dataHost/schema config; frontend session isolation mapped incorrectly to the backend; code that passes e.g. TRANSACTION_NONE or a driver-specific constant into the PG backend connection.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• invalid param ,connection request db is
• Invalid DataSource
• txIsolation
• the select proess err ,the SelectResponse is empty
• offer data error!

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/4a6aeeee071f1293. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/backend/postgresql/PostgreSQLBackendConnection.java:125

	 * @param
	 * @param txIsolation
	 */
	private static void getTxIsolationCommand(StringBuilder sb, int txIsolation) {
		switch (txIsolation) {
		case Isolations.READ_UNCOMMITTED:
			sb.append("SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;");
			return;
		case Isolations.READ_COMMITTED:
			sb.append("SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;");
			return;
		case Isolations.REPEATED_READ:
			sb.append("SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;");
			return;
		case Isolations.SERIALIZABLE:
			sb.append("SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE;");
			return;
		default:
			throw new UnknownTxIsolationException("txIsolation:" + txIsolation);
		}
	}

	private Object attachment;

	private volatile boolean autocommit=true;

	private volatile boolean txReadonly=false;

	private volatile boolean borrowed;

	protected volatile String charset = "utf8";


	/***
	 * 当前事物ID
	 */
	private volatile String currentXaTxId;

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