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 is shape-dependent. The shapes and associated transaction size limits (bytes) are as follows:
  • MySQL.VM.Standard.E3.1.8GB: 85899346
  • MySQL.VM.Standard.E3.1.16GB: 171798692
  • MySQL.VM.Standard.E3.2.32GB: 343597384
  • MySQL.VM.Standard.E3.4.64GB: 687194767
  • MySQL.VM.Standard.E3.8.128GB: 1073741824
  • MySQL.VM.Standard.E3.16.256GB: 1073741824
  • MySQL.VM.Standard.E3.24.384GB: 1073741824
  • MySQL.VM.Standard.E3.32.512GB: 1073741824
  • MySQL.VM.Standard.E3.48.768GB: 1073741824
  • MySQL.VM.Standard.E3.64.1024GB: 1073741824
• If a HeatWave 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 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.