change the default value of the default_time_zone parameter - ApsaraDB RDS

Starting February 1, 2025, the default value of the default_time_zone parameter of an ApsaraDB RDS for MySQL instance is changed from SYSTEM to the default time zone of the region in which the RDS instance resides.

Background information

The time zone of an RDS instance is specified by the default_time_zone parameter. The default value of the parameter is SYSTEM, which specifies that the RDS instance has the same time zone as the host of the instance.

If the value of the default_time_zone parameter is SYSTEM, the following risks may occur:

Instance performance degradation
If your workloads frequently use TIMESTAMP-type fields, lock contention may occur due to time zone conversion. This may cause performance fluctuations.
Time inconsistency between the primary and secondary RDS instances
If your RDS instance uses local disks, the time on the primary and secondary RDS instances may be different due to time zone inconsistency in extreme scenarios. This may cause data inconsistency.

Parameter configuration adjustment

To ensure the stability and performance of an RDS instance, the following adjustments are applied to the default_time_zone parameter:

Adjustment of the default parameter value for new RDS instances (starting February 1, 2025)

Changes
The default value of the default_time_zone parameter is changed from SYSTEM to the standard time zone of the region in which the RDS instance resides. For example, if the RDS instance resides in the China (Shanghai) region, the default value of this parameter is Asia/Shanghai. For more information about other regions, see Time zones.
Affected instances
The adjustment applies only to new RDS instances regardless of the storage type. Existing RDS instances that use cloud disks use the original configuration.

Adjustment of the permissions to modify parameters (starting February 1, 2025)

Changes
You cannot change the value of the default_time_zone parameter to SYSTEM for RDS instances that use local disks.
Affected instances
After the adjustment, you can set the parameter only to the standard time zone of RDS instances that use local disks. For example, you can set the parameter to +08:00 or Asia/Shanghai.

Adjustment of the parameter configuration for existing RDS instances (from March 12, 2025 to May 30, 2025)

Operation objects
Existing RDS instance that use local disks and SYSTEM for the default_time_zone parameter.
Change methods
- Automatic change: Starting March 12, 2025, Alibaba Cloud adjusts the parameter value for RDS instances in batches. During the O&M window, the system automatically changes the parameter value to the time zone offset that matches the instance region. For example, the time zone of an RDS instance in the China (Shanghai) region is CST. In this case, the system changes the value to +08:00. No manual operations are required.
- Manual change: If you want to specify a custom time zone or adjust the time, you can change the value of the default_time_zone parameter in the ApsaraDB RDS console and restart the instance. For more information, see Change the time zone.
Impacts
- Automatic change: You do not need to restart your RDS instance, and services are not interrupted.
- Manual change: You must restart your RDS instance, which may cause service interruptions. We recommend that you perform this operation during off-peak hours and make sure that your application is configured to automatically reconnect to your RDS instance.
- The operating system time and MySQL time field storage are not affected. Only the calculation rules of time zones are updated.