Description:
While using mysql-connector-python, with the C extension, some calls to mysqlconnect fail with the following stack trace:
Traceback (most recent call last):
File "/usr/local/lib64/python3.12/site-packages/mysql/connector/connection_cext.py", line 365, in _open_connection
self._cmysql.connect(**cnx_kwargs)
_mysql_connector.MySQLInterfaceError: Authentication plugin 'mysql_native_password' cannot be loaded: it is already loaded
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/usr/local/lib/python3.12/site-packages/app/lib/sql/mysql_store.py", line 41, in __init__
self._connection = connect(
^^^^^^^^
File "/usr/local/lib64/python3.12/site-packages/mysql/connector/pooling.py", line 322, in connect
return CMySQLConnection(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib64/python3.12/site-packages/mysql/connector/connection_cext.py", line 153, in __init__
self.connect(**kwargs)
File "/usr/local/lib64/python3.12/site-packages/mysql/connector/abstracts.py", line 1529, in connect
self._open_connection()
File "/usr/local/lib64/python3.12/site-packages/mysql/connector/connection_cext.py", line 370, in _open_connection
raise get_mysql_exception(
mysql.connector.errors.DatabaseError: 2059 (HY000): Authentication plugin 'mysql_native_password' cannot be loaded: it is already loaded
How to repeat:
This happens in the following context:
* In a multi-threaded web application;
* When concurrent calls to mysql.connector.connect are being made;
* When there was previously no activity (and thus, no previously successful calls to mysql.connector.connect) in the same process;
Suggested fix:
After reviewing the source code for mysql-connector-python as published on github, I have a working theory for where the issue comes from:
https://github.com/mysql/mysql-connector-python/blob/9.2.0/mysql-connector-python/src/mysq...
mysql.connector.connect eventually calls into the MySQL_connect C function, and this function calls the mysql_init function in a GIL-unlocked block:
```
Py_BEGIN_ALLOW_THREADS
if (self->connected) {
self->connected = 0;
mysql_close(&self->session);
}
mysql_init(&self->session);
Py_END_ALLOW_THREADS
```
This means that the mysql_init method can be called concurrently in a multi-threaded python context. However, when the library has never been initialized in the process, mysql_init ends up calling mysql_library_init, which is documented in https://dev.mysql.com/doc/c-api/9.2/en/c-api-threaded-clients.html as being not thread-safe.
I can think of two big ways of solving that:
* Either adding a call to mysql_library_init in the module initialization function https://github.com/mysql/mysql-connector-python/blob/9.2.0/mysql-connector-python/src/mysq... ;
* Or adding a boolean in MySQL_connect that checks whether mysql_library_init has already been called in the current process, and to call that function only if it has not been called (this boolean and check must be made in a thread-safe way)
Right now, I am going to work around this bug by managing a lock around calls to connect.
© 2025, Oracle Corporation and/or its affiliates
Description: While using mysql-connector-python, with the C extension, some calls to mysqlconnect fail with the following stack trace: Traceback (most recent call last): File "/usr/local/lib64/python3.12/site-packages/mysql/connector/connection_cext.py", line 365, in _open_connection self._cmysql.connect(**cnx_kwargs) _mysql_connector.MySQLInterfaceError: Authentication plugin 'mysql_native_password' cannot be loaded: it is already loaded The above exception was the direct cause of the following exception: Traceback (most recent call last): File "/usr/local/lib/python3.12/site-packages/app/lib/sql/mysql_store.py", line 41, in __init__ self._connection = connect( ^^^^^^^^ File "/usr/local/lib64/python3.12/site-packages/mysql/connector/pooling.py", line 322, in connect return CMySQLConnection(*args, **kwargs) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/local/lib64/python3.12/site-packages/mysql/connector/connection_cext.py", line 153, in __init__ self.connect(**kwargs) File "/usr/local/lib64/python3.12/site-packages/mysql/connector/abstracts.py", line 1529, in connect self._open_connection() File "/usr/local/lib64/python3.12/site-packages/mysql/connector/connection_cext.py", line 370, in _open_connection raise get_mysql_exception( mysql.connector.errors.DatabaseError: 2059 (HY000): Authentication plugin 'mysql_native_password' cannot be loaded: it is already loaded How to repeat: This happens in the following context: * In a multi-threaded web application; * When concurrent calls to mysql.connector.connect are being made; * When there was previously no activity (and thus, no previously successful calls to mysql.connector.connect) in the same process; Suggested fix: After reviewing the source code for mysql-connector-python as published on github, I have a working theory for where the issue comes from: https://github.com/mysql/mysql-connector-python/blob/9.2.0/mysql-connector-python/src/mysq... mysql.connector.connect eventually calls into the MySQL_connect C function, and this function calls the mysql_init function in a GIL-unlocked block: ``` Py_BEGIN_ALLOW_THREADS if (self->connected) { self->connected = 0; mysql_close(&self->session); } mysql_init(&self->session); Py_END_ALLOW_THREADS ``` This means that the mysql_init method can be called concurrently in a multi-threaded python context. However, when the library has never been initialized in the process, mysql_init ends up calling mysql_library_init, which is documented in https://dev.mysql.com/doc/c-api/9.2/en/c-api-threaded-clients.html as being not thread-safe. I can think of two big ways of solving that: * Either adding a call to mysql_library_init in the module initialization function https://github.com/mysql/mysql-connector-python/blob/9.2.0/mysql-connector-python/src/mysq... ; * Or adding a boolean in MySQL_connect that checks whether mysql_library_init has already been called in the current process, and to call that function only if it has not been called (this boolean and check must be made in a thread-safe way) Right now, I am going to work around this bug by managing a lock around calls to connect.