[Maria-discuss] The relay-log is not fluashed after the slave-relay-log.999999 showed

Hello, dear users. I am using MariaDB 10.0.14 at CentOS 6.5. And, as I mentioned at the title of this question, the relay-log is not flushed after the slave-relay-log.999999 showed when using "Salve_parallel_threads:10" setting. like showed blow. - binlog_format: ROW - Slave_parallel_threads:10 Everything are working fine except the "slave-relay-log.******" files continue to exist at the disk which will finally cause the disk full. If I change the value of Slave_parallel_threads setting from 10 to 0, the log will be flushed. Howevery "PK duplicate warning" error logs come next. Is there any setting should be used with Slave_parallel_threads setting? Any help will be great. Best regareds, - Jasung