Resolving MySQL Error 1228 (ER_LOCAL_VARIABLE): Understanding Session vs. Global Variables

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Encountering Error 1228 – SQLSTATE: HY000 (ER_LOCAL_VARIABLE) in MySQL can be a bit confusing. This error message indicates that there’s an attempt to set a session-specific system variable at a global level, which is not allowed. MySQL differentiates between variables that can be set globally for all connections and those that are specific to the current session. This guide will help you understand the error and provide solutions to fix it.

Understanding Error 1228

In MySQL, system variables can have a global or session scope. Global variables affect the operation of the server as a whole, whereas session variables only affect the current connection. Error 1228 arises when you mistakenly try to apply a session-level variable change to the global scope.

Diagnosing the Error

The error message you receive will include the name of the variable that you’re trying to set incorrectly. For example:

Variable 'sort_buffer_size' is a SESSION variable and can't be used with SET GLOBAL.

Fixing the Error

To resolve this error, you need to ensure that you’re setting the variable at the correct scope. Here are some examples and how to address them:

1. Incorrectly Setting a Session Variable as Global

If you try to set a session variable globally, you’ll encounter Error 1228:

SET GLOBAL sort_buffer_size = 1048576;

To fix this, set the variable at the session level:

SET SESSION sort_buffer_size = 1048576;

Or, if it’s meant to be a global change for new connections:

SET GLOBAL sort_buffer_size = 1048576;

2. Using the Wrong Variable Name

Sometimes, you might use the wrong variable name that doesn’t exist as a global variable:

SET GLOBAL max_allowed_packet = 16777216;

If max_allowed_packet is not a recognized global variable, you’ll see Error 1228. Make sure you’re using the correct variable name and scope:

SET GLOBAL max_allowed_packet = 16777216; -- Correct usage if max_allowed_packet is a global variable

3. Attempting to Change Read-Only Variables

Some global variables are read-only and can’t be changed at runtime:

SET GLOBAL innodb_buffer_pool_size = 536870912;

If innodb_buffer_pool_size is read-only, you can’t set it with SET GLOBAL. Instead, you need to change it in the MySQL configuration file (my.cnf or my.ini) and restart the server:

[mysqld]
innodb_buffer_pool_size = 536870912

4. Misunderstanding the Scope of Variables

Ensure you understand which variables are global, session, or both. For example:

SET GLOBAL autocommit = 0; -- Correct if autocommit has a global scope

Consult the MySQL documentation to confirm the scope of the variable you’re trying to set.

Preventive Measures

To prevent this error:

  • Always check the scope of a variable before attempting to set it.
  • Refer to the MySQL documentation for a comprehensive list of system variables and their scopes.
  • Use SHOW VARIABLES to understand current settings and their scopes:
SHOW VARIABLES LIKE 'variable_name';

Conclusion

Understanding the scope of system variables in MySQL is crucial to avoid Error 1228. When configuring your server, make sure you apply changes at the correct level—global or session. Properly managing these variables will help maintain a stable and efficient database environment. If you need further clarification on variable scope, the MySQL documentation is a valuable resource. For persistent issues or complex configurations, seeking the guidance of a database administrator is recommended.

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