Got below error from application end.
SQL state [HY001]; error code ; (conn=15945) Out of sort memory, consider increasing server sort buffer size; nested exception is java.sql.SQLException: (conn=15945) Out of sort memory, consider increasing server sort buffer size
Detailed dig down on the MariaDB error log found the below error.
[ERROR] mariadbd: Out of sort memory, consider increasing server sort buffer size
With reference of the above error it found that the sort_merge_passes global status variable has a high value over 600 on Galera node1. Thus it is definitive that the value of sort_buffer_size global system variable value needs to be increased.
Increase the value of sort_buffer_size.
There are no specific formula of how much to increase the value of sort_buffer_size but start with a small portion depending on the nature of your application sorting data size. You can increase with an increment of 2M, 4M, 16M, 32M, 128M at a time depending on your available physical memory and monitor the impact. Putting this variable at a high value GLOBALLY may leads to performance degradation as larger values may significantly slow down memory allocation, then set the value at SESSION level not GLOBALLY.