Saw message regarding "The database is using the doublebuffer" during mysql update

The message you encountered during your MySQL upgrade is related to a feature called RDS Optimized Writes. This feature is designed to improve write performance for MySQL databases on Amazon RDS by eliminating the need for the doublewrite buffer.

Typically, MySQL uses a doublewrite buffer to prevent partial page write errors that can occur during hardware failures or power outages. While this provides data protection, it also results in extra write operations, which can impact performance.

RDS Optimized Writes allows databases to write only once when flushing data to durable storage, potentially achieving up to two times higher write transaction throughput. This is particularly beneficial for write-heavy workloads.

The message you saw indicates that your database is currently using the doublewrite buffer, and RDS Optimized Writes is not compatible with your current storage configuration. This could be due to several factors, such as:

1. The specific DB engine version you're using
2. The instance class of your database
3. The storage type or configuration

The fact that you didn't see this message in your non-production instances could be due to differences in these factors between your production and non-production environments.

While this message doesn't indicate a problem with your database, it does suggest that you might have an opportunity to improve write performance if you can configure your database to use RDS Optimized Writes. To do this, you may need to:

1. Ensure you're using a supported MySQL version (8.0 and later)
2. Use a compatible instance class (those using the AWS Nitro System)
3. Set the 'rds.optimized_writes' parameter to 'AUTO' in your DB parameter group

If you're interested in enabling this feature, you might need to perform a storage configuration upgrade, which can be done through a blue/green deployment process.

Remember, while RDS Optimized Writes can offer performance benefits, your current setup with the doublewrite buffer is still providing the necessary data protection. The message is more informational, alerting you to a potential optimization opportunity rather than indicating a problem.

Sources
Replication lag issue during and after upgrade from mysql5.7 to mysql 8.0.36 | AWS re:Post
Amazon RDS event categories and event messages - Amazon Relational Database Service
Improving write performance with RDS Optimized Writes for MySQL - Amazon Relational Database Service