I'm looking at the Performance Insights for MySQL Aurora on AWS and among the top queries I see:
SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
These statements don't appear in my code anywhere, I couldn't find them in the HikariCP implementation, in the MySQL/J driver or the JDBC connection string. I was able to confirm that the last query
SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED occurs when a new connection is created. These queries are wasteful since they come from a reader instance. Any ideas on how to trace and stop this?
This is with HikariCP 3.4.5, mysql connector 8.0.11 and MySQL 5.7. Below is a screenshot of what Performance Insights shows. Note that setting session parameters is 4 of the top 5 queries by Average Active Sessions. The wait event in green is
wait/io/aurora_respond_to_client, so I guess it's just waiting for the client to confirm receipt.