MySQL raises ER_STD_UNKNOWN_EXCEPTION when an unexpected C++ std::exception escapes internal code, causing runtime error 3054 (SQLSTATE HY000).
ER_STD_UNKNOWN_EXCEPTION (MySQL error 3054) indicates the server caught an unexpected C++ exception. Check error logs, disable or update faulty plugins, and upgrade MySQL to remove the unknown exception.
ER_STD_UNKNOWN_EXCEPTION
The error message "Unknown exception: %s in function %s" appears when the MySQL server catches an unexpected C++ std::exception that bubbles out of internal code. MySQL converts that unhandled exception into runtime error 3054 with SQLSTATE HY000, signalling that something went wrong inside the server rather than in your SQL.
Because the failure happens in the server process, client SQL usually looks correct. The error is still critical because it aborts the statement and can indicate corrupted data, faulty plugins, or a server bug. Understanding and isolating the root cause is essential to restore stability and prevent data loss.
MySQL throws ER_STD_UNKNOWN_EXCEPTION when an internal function catches a generic std::exception without a dedicated error handler. This often points to bugs in storage engine code, UDFs, plugins, or third-party patches that raise unexpected exceptions.
The error can also appear after out-of-memory conditions, invalid pointer dereference, or other low-level faults that trigger standard library exceptions. Upgrades between minor versions sometimes surface latent issues when old plugins are not recompiled.
First, reproduce the problem in a test environment with general and error logs activated. Identify the SQL statement that triggers the crash and note the function name reported in the error text. Check the MySQL error log for a matching stack trace.
Second, disable or upgrade the component named in the stack trace. For a storage engine, run ALTER TABLE ... ENGINE=InnoDB to migrate data. For a UDF or plugin, uninstall it with UNINSTALL PLUGIN or recompile it against the current MySQL headers.
InnoDB corruption: run CHECK TABLE and mysqlcheck, then recover from backup or rebuild the table.
Outdated UDF: recompile the shared object with the correct MySQL version and reinstall.
Custom plugin fault: comment the plugin-load line in my.cnf and restart to verify that the error disappears.
Keep all plugins, UDFs, and storage engines compiled against the exact server version in production. Use CI to rebuild after every upgrade.
Enable MySQL's error log and slow query log so anomalies are caught early. Run regular CHECK TABLE and backup verification to detect corruption before it reaches users.
Error 1105 (HY000) unknown error - generic catch-all similar but without std::exception.
Error 2013 Lost connection to MySQL server during query - can surface when ER_STD_UNKNOWN_EXCEPTION forces a server abort. Fixing the underlying exception removes both errors.
Plugins or UDFs compiled for older MySQL versions may raise unexpected std::exceptions when called by newer server binaries.
A faulty storage engine implementation or corrupted page can trigger low-level C++ exceptions that bubble up as error 3054.
Running out of memory or file descriptors may cause std::bad_alloc or related exceptions inside MySQL, leading to ER_STD_UNKNOWN_EXCEPTION.
Unverified patches that modify server source code can introduce undefined behavior and unexpected exceptions.
Another catch-all runtime error that signals an unspecified problem inside MySQL.
Often appears when the server aborts mid execution due to ER_STD_UNKNOWN_EXCEPTION.
Networking issues can occur after server restarts triggered by unknown exceptions.
Not always, but storage engine corruption is a common trigger. Run CHECK TABLE and review logs to confirm.
No. The exception indicates unstable server state. Investigate immediately to avoid crashes or data loss.
Enable the error log and set mysqld to start with --gdb or --core-file-size=unlimited, then inspect the core with gdb.
Galaxy centralizes vetted SQL and surfaces execution errors in its editor, making it easier to trace failing queries and share fixes across the team quickly.
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