12.9 Limitations for High Availability

A high availability DB system has certain limitations.

• 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 clients.
• The maximum size of transaction depends on the amount of memory of the shape and is listed in Limitations for High Availability.

  Table 12-2 Maximum Size of Transaction for a High Availability DB System

  Shape Memory (GiB)	Maximum Transaction Size (Bytes)
  16	171,798,692
  32	343,597,384
  64	687,194,767
  256	1,073,741,824

• The maintenance of a high availability DB system requires rolling upgrades, for which there is 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.
• HeatWave Clusters, as well as any features that require a HeatWave Cluster (for example, HeatWave Lakehouse, HeatWave GenAI, or HeatWave AutoML), are not currently supported on a high availability DB system.

• When using a Query PrivateLink endpoint, failovers and switchovers take longer than on a public endpoint.

  To reduce Query PrivateLink endpoint downtime on failovers or switchovers, configure your application by setting the value of the connect_timeout parameter to a small value (for example, 5 seconds) and by making it retry always upon connection failures.

• The Bulk Ingest Feature is not supported on the DB System.
• Configuration changes and storage resize for high availability DB Systems are not supported.
• High availability cannot be enabled on a standalone DB System with PrivateLink(s) configured. Delete the PrivateLinks, and then recreate them after enabling high availability.
• High availability cannot be disabled on a high availability DB System.

See also the limitations described in Restoring a Backup of a High Availability DB System and Inbound Replication to a High Availability DB System.