Constraints

Constraints on Usage

Before enabling ALT, contact customer service to apply for the required permissions.
This feature can only be enabled for a Primary/Standby instance meeting all of the following requirements: Its Failover Priority is set to Reliability, read/write splitting is enabled, and it is connected through a read/write splitting address.
This feature is available only for RDS for MySQL 5.7.
The supported RDS for MySQL and proxy kernel versions are as follows:
- RDS for MySQL 5.7.37.1 or later (For versions earlier than 5.7.37.1, manually upgrade the kernel to the latest version by referring to Upgrading a Minor Version.)
- Proxy 2.7.5.0 or later (For versions earlier than 2.7.5.0, manually upgrade the kernel to the latest version by referring to Upgrading the Kernel Version of Database Proxy.)

Constraints on Scenarios

For details about syntax and function constraints of the database proxy, see Suggestions on Using Database Proxy.
ALT does not support the Prepare protocol.
Enabling ALT makes your instance lose support for some system variable values.
- innodb_ft_user_stopword_table: It can only be set to NULL.
- transaction_write_set_extraction: It can only be set to OFF.
- profiling: It cannot be set to 1 or ON.
ALT does not support Transparent Data Encryption (TDE).
ALT is unavailable when any of the following proxy capabilities is enabled:
- Session-level connection pool
- Any column containing more than 16 MB of data
- Prepared statement cache
ALT does not support temporary tables created by users.
ALT is not supported in the following scenarios where a secure transaction boundary cannot be reached:
- InnoDB transaction blocks are not committed in a timely manner.
- There are unreleased table locks, user locks, backup locks, and binlog locks.
- XA transactions are not committed or rolled back.
ALT cannot be used for a DB instance with a long replication delay.
During a primary/standby switchover, minor version upgrade, or instance class change, if data consistency cannot be reached between the primary and standby instances in a timely manner due to replication delay, your DB instance may become read-only or database connection may be interrupted.
ALT will be likely to fail if a switchover, minor version upgrade, or instance class change occurs frequently within a short period of time.
ALT is not supported when the multi-proxy function is enabled.