What causes "msg == null ? e.getClass().getSimpleName() : msg" in MyCATApache/Mycat-Server?

Inspect the server log line '... error: ' for the underlying cause and stack trace.

ER_PARSE_ERROR

ER_PARSE_ERROR

Error message

msg == null ? e.getClass().getSimpleName() : msg

What it means

ExplainHandler.getRouteResultset() runs EXPLAIN statements through the router service and converts any exception into an ER_PARSE_ERROR error packet written to the manager/client connection, using e.getMessage() or the exception class simple name when null. It tells the developer that Mycat could not route the statement being explained.

Solutions

Inspect the server log line '... <stmt> error: <exception>' for the underlying cause and stack trace.
Fix the explained SQL or the corresponding schema/rule configuration so route() succeeds.
If the message is a bare class name, locate the NPE/IAE in the stack trace and fix the missing configuration it points to.

Example fix

// before
EXPLAIN INSERT INTO t_seq VALUES (NEXT VALUE FOR MYCATSEQ_GLOBAL); // malformed sequence usage -> router exception
// after
// configure the sequence in sequence_conf.properties / rule.xml, then:
EXPLAIN INSERT INTO t_seq (name) VALUES ('a');

Defensive patterns

Strategy: try-catch

Validate before calling

// verify target table is routable before issuing EXPLAIN
String table = resolveTableName(stmt);
if (!mycatSchemaTables.contains(table)) {
    System.err.println("cannot EXPLAIN: table missing from schema.xml: " + table);
}

Try / catch

try (Statement st = conn.createStatement()) {
    st.execute("EXPLAIN " + sql);
} catch (SQLException e) {
    if (e.getErrorCode() == 1064) {
        // Mycat router rejected the explained statement; read server.log 'error:' line
        LOGGER.error("EXPLAIN routing failed for: " + sql, e);
    } else {
        throw e;
    }
}

Prevention

Use EXPLAIN only on tables already declared in schema.xml.
Simplify the explained SQL first; complex subqueries/hints may be unparseable by the router.
Read the manager/server log line '... error: <exception>' for the true cause.
Keep Mycat sequence configuration valid when explaining statements using NEXT VALUE FOR.

When it happens

Trigger: Any Exception from MycatServer.getInstance().getRouterservice().route(...) while processing an EXPLAIN statement: unsupported syntax, missing schema/table routing config, router internal errors; null-message exceptions yield just the class name in the error packet.

Common situations: Using EXPLAIN to debug sharding of a table that is missing from schema.xml; EXPLAIN of SQL the Druid-based parser cannot parse; sequence (isMycatSeq) or hint handling throwing on malformed input.

Understand the failure class

Background: "query failed", "%w: SQL error" — wrapped database query errors in Go libraries explained — this error's family across 3 libraries.

Related errors

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/d3c09b37335c8f03. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/server/handler/ExplainHandler.java:156

			c.writeErrMessage(ErrorCode.ER_BAD_DB_ERROR, "Unknown database '"
					+ db + "'");
			return null;
		}
		try {

            if(ServerParse.INSERT==sqlType&&isMycatSeq(stmt, schema))
            {
                c.writeErrMessage(ErrorCode.ER_PARSE_ERROR, "insert sql using mycat seq,you must provide primaryKey value for explain");
                return null;
            }
            SystemConfig system = MycatServer.getInstance().getConfig().getSystem();
            return MycatServer.getInstance().getRouterservice()
					.route(system,schema, sqlType, stmt, c.getCharset(), c);
		} catch (Exception e) {
			StringBuilder s = new StringBuilder();
			logger.warn(s.append(c).append(stmt).toString()+" error:"+ e);
			String msg = e.getMessage();
			c.writeErrMessage(ErrorCode.ER_PARSE_ERROR, msg == null ? e
					.getClass().getSimpleName() : msg);
			return null;
		}
	}

    private static boolean isMycatSeq(String stmt, SchemaConfig schema)
    {
        if(pattern.matcher(stmt).find()) {
			return true;
		}
        SQLStatementParser parser =new MySqlStatementParser(stmt);
        MySqlInsertStatement statement = (MySqlInsertStatement) parser.parseStatement();
        String tableName=   statement.getTableName().getSimpleName();
        TableConfig tableConfig= schema.getTables().get(tableName.toUpperCase());
        if(tableConfig==null) {
			return false;
		}
        if(tableConfig.isAutoIncrement())

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