wsrep_streaming_log file size continues to grow

It is observed that the system table "mysql.wsrep_streaming_log" file size continues to grow when loading a large amount of data. After restarting the DB server, the file size still remains. It needs to optimize the table in order to clean up the file size.

To repeat the scenario:

1. In DB server:
set global wsrep_trx_fragment_size=1073741823;
2. Create a table.
3. Record the table file size of mysql/wsrep_streaming_log.ibd in mydata directory.
4. Load data to the table within a single transaction having total data size <= 1073741823.
5. Record the table file size of mysql/wsrep_streaming_log.ibd again, the size grows accordingly.
6. Restart the DB server, the file size does not decrease.
7. Run optimize the table, the file size decrease.