apache/seatunnel · warning · IOException

Error while closing Databend source reader

Error message

Error while closing Databend source reader

What it means

This error is thrown by DatabendSourceReader.close() when releasing the JDBC Statement or Connection fails with a SQLException during reader shutdown. The original SQLException is wrapped in an IOException so it surfaces as a source-reader close failure rather than a read failure. It usually indicates the connection was already broken or already closed by the time cleanup ran.

Source

Thrown at seatunnel-connectors-v2/connector-databend/src/main/java/org/apache/seatunnel/connectors/seatunnel/databend/source/DatabendSourceReader.java:316

                        typeName);
                return BasicType.STRING_TYPE;
        }
    }

    @Override
    public void close() throws IOException {
        try {
            if (resultSet != null) {
                resultSet.close();
            }
            if (statement != null) {
                statement.close();
            }
            if (connection != null) {
                connection.close();
            }
        } catch (SQLException e) {
            throw new IOException("Error while closing Databend source reader", e);
        }
    }
}

View on GitHub (pinned to cf67b549a7)

Solutions

1. Inspect the wrapped SQLException cause: if it reports 'connection already closed' or socket timeout, the close failure is benign and the reader was effectively cleaned up - fix the underlying connection stability instead
2. Enable JDBC keepalive/heartbeat and tune Datasense/proxy idle timeouts so connections survive long reads
3. Wrap each close() (statement, connection) in its own try-catch so one resource failing to close does not abort the other's cleanup
4. Verify network stability between the SeaTunnel worker and Databend (firewalls, NAT idle timeouts, Databend query timeouts)

Example fix

// before
statement.close();
connection.close();
// after
try {
    if (statement != null) statement.close();
} catch (SQLException e) {
    log.warn("Failed to close Databend statement", e);
}
try {
    if (connection != null) connection.close();
} catch (SQLException e) {
    log.warn("Failed to close Databend connection", e);
}

// before closing: check connection validity
if (connection != null && !connection.isClosed()) {
    connection.close();
}

boolean isOpen(Connection c) { try { return c != null && !c.isClosed(); } catch (SQLException e) { return false; } }

try { reader.close(); } catch (IOException e) {
    if (e.getCause() instanceof SQLException && "08003".equals(((SQLException) e.getCause()).getSQLState())) {
        log.warn("Connection already closed; ignoring", e);
    } else { throw e; }
}

When it happens

Trigger: Calling close() on the reader while the JDBC connection to Databend has been dropped (network cut, Databend restarted, idle timeout) so connection.close() throws; closing an already-closed connection; driver-level socket errors during statement.close().

Common situations: Long-running batch jobs where Databend or a LB closes idle connections; container network interruptions; job cancellation racing with connection teardown; duplicate close() calls on the same reader.

Understand the failure class

Background: Database query failed: Internal Server Error 500s wrapping SQL, Prisma, and connection failures — what to check first — this error's family across 16 libraries.

Related errors

• failed to close arrow stream reader.
• DRIVER_NOT_FOUND
• CONNECT_FAILED
• SQL_OPERATION_FAILED
• CONNECT_FAILED

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/5662c2f1b165106f. Report an issue: GitHub.