A high availability DB system has certain limitations.

• A high availability DB system performs rolling upgrades, which has a brief period of downtime before the newly promoted MySQL instance resumes connections. Each MySQL instance is upgraded separately. See Maintenance of a High Availability DB System.
• High availability is supported for version 8.0.24 of MySQL, or higher. You cannot create a highly available DB system using a backup from a DB system with an earlier version.
• You can access the MySQL instance that functions as the primary instance only. You cannot access the other two secondary instances directly, using MySQL Shell, or any other such client.
• The maximum size of transaction depends to the amount of memory of the shape. The memory of the shapes and associated transaction size limits (in bytes) are as follows:
  • 8GB: 85,899,346
  • 16GB: 171,798,692
  • 32GB: 343,597,384
  • 64GB: 687,194,767
  • 128GB or more: 1,073,741,824
• If a HeatWave cluster load or reload operation is going on, enabling or disabling high availability can fail. It is recommended to not enable or disable high availability while a HeatWave cluster load or reload operation is going on.
• Prior to MySQL 8.3.0-u2, you cannot enable high availability on a DB system with HeatWave Lakehouse enabled.