RDS Performance Insights doesn't display all top SQL stats

Question

We have an issue with Performance Insights for one of our RDS instances. We have two mysql 5.7.38, db.m5.xlarge instances. Both DB uses the same parameter group, security groups and the monitoring role. One instance is a primary, and the second is a read-only replica. We enabled Performance Insights and Enhanced monitoring on both of them.

Unfortunately, only the read-only replica shows full stats for top SQL queries.

Primary DB Enter image description here

Read-only replica Enter image description here

I have trierd disable and enable Performance Insights and reboot instance, no luck so far.

Unfortunately, only the read-only replica shows full stats for top SQL queries.

Primary DB 
![Enter image description here](/media/postImages/original/IMguOEZ3yZQvmkSmy2eHwXSA)

Read-only replica
![Enter image description here](/media/postImages/original/IMztI8SbleRqm9tDaOl7kVZg)

I have trierd disable and enable Performance Insights and reboot instance, no luck so far.

Answer

This is because the query distribution differs for Primary and read only replica. **Primary serves as the Writer endpoint** and can also server read requests. **Read replica only handles the read queries**, your application is sending all Select requests to read replica thats the reason you see all the **Select** queries in the stats.

RDS Performance Insights doesn't display all top SQL stats

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