Is it possible that SELECT queries will cause a flow control issue for the Galera Cluster?

MySQL & MariaDB Percona XtraDB Cluster 8.x
1

Can someone answer the below question?

Is it possible that SELECT queries will cause a flow control issue for the Galera Cluster?

2

Flow control manages write activity; nothing to do with read activity. SELECT’s are read-only and are local to a node. I don’t believe a SELECT query can cause flow control for these reasons.

3

Thanks @matthewb for the detailed information.

How can we find which write query is causing the flow control issue?

4

You could explore the pt-stalk tool, which can collect some details related to the database (processlist, engine status etc) and system once the defined --variable and --threshold conditions are met, like wsrep_flow_control_paused > 0 or wsrep_flow_control_active is active etc…

5

@Naresh9999,
I recommend you configure PMM for each node. This will allow you to track flow control (if that is indeed your issue, PMM will verify this) and correlate it to queries running in your system. Be sure to set long_query_time=0 to track all queries.

6

Thanks @matthewb and @Abhinav_Gupta

I’ll do my best to come up with a solution using your suggestions.