System Variables¶

System variables control the behavior of a session or the entire instance engine. Use SET to change them, subject to privileges and whether a variable can be changed dynamically, and use SHOW VARIABLES to inspect them.

Global and session scopes¶

Scope	Meaning
Global (GLOBAL)	Affects the default behavior of new sessions. Some values persist for the instance lifecycle.
Session (SESSION)	Applies only to the current connection and expires when it disconnects.
Both	Has both a global default and a session override.

SHOW VARIABLES;
SHOW VARIABLES LIKE 'sql_mode';
SHOW GLOBAL VARIABLES;
SHOW SESSION VARIABLES LIKE '%timeout%';

SET SESSION autocommit = 0;
SET GLOBAL max_allowed_packet = 33554432;  -- Requires sufficient privileges, and the variable must support dynamic modification

Custom user variables such as @var differ from system variables. They temporarily store scalar values within a session. Refer to client usage and statements such as SET @a = ....

Common variables¶

The following table lists variables commonly encountered in the documentation and product. Refer to SHOW VARIABLES for the complete list.

Variable	Typical purpose	Notes
`autocommit`	Enables automatic commits	Transaction scripts commonly disable it temporarily.
`sql_mode`	SQL mode set	Affects strictness, GROUP BY behavior, and more.
`character_set_` / `collation_`	Character sets and collations	A common default is `utf8mb4`.
`time_zone`	Session time zone	Affects `TIMESTAMP` display and conversion.
`lower_case_table_names`	Table-name case behavior	Commonly 1 (case-insensitive) and usually should not be changed arbitrarily.
`max_allowed_packet`	Maximum packet size in bytes	Increase it for large results or statements.
`interactive_timeout` / `net_write_timeout`	Idle and write timeouts	Relevant to long-lived connections and slow networks.
`auto_increment_increment` / `auto_increment_offset`	Auto-increment step and offset
`foreign_key_checks`	Enables foreign-key checks	Can be disabled temporarily during bulk loading after consistency risks are assessed.
`save_query_result` / `query_result_*`	Query-result persistence	MatrixOne extension capabilities
`sql_safe_updates`	Safe updates	Restricts updates and deletes without a key or WHERE clause.
Password / login policy variables	Complexity, failure limits, allowlists, and more	Related to instance security policies

Query-result extensions¶

If query-result persistence is enabled for the instance:

save_query_result: Whether to save results.
query_result_maxsize / query_result_timeout: Size and retention-time limits.

Whether these capabilities are available to your tenant depends on the console and SHOW VARIABLES.