The client connection is off abnormally, causing the sort task hung

[sevenFH]

1、sql:
select * from mytest.sbtest1 group by k limit 1
2、sysbench pressure test.

[root@10-186-23-13 sysbench-0.5]# sysbench --test=db2/select_group_by.lua --oltp-table-size=100 --num-threads=1 --mysql-user=test --mysql-password=test --mysql-host=10.186.23.12 --mysql-port=8066 --mysql-db=mytest --report-interval=1 run
sysbench 0.5:  multi-threaded system evaluation benchmark

Running the test with following options:
Number of threads: 1
Report intermediate results every 1 second(s)
Random number generator seed is 0 and will be ignored


Threads started!

[   1s] threads: 1, tps: 0.00, reads/s: 146.98, writes/s: 0.00
[   2s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[   3s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[   4s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[   5s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[   6s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[   7s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[   8s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[   9s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[  10s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[  11s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00
[  12s] threads: 1, tps: 0.00, reads/s: 0.00, writes/s: 0.00

3、dble.log:

[root@10-186-23-12 logs]# tail -f dble.log | grep 'close'
2018-01-10 16:09:55.325 DEBUG [BusinessExecutor0] (com.actiontech.dble.net.AbstractConnection.close(AbstractConnection.java:469)) - close connection,reason:no handler ,MySQLConnection [id=4, lastTime=1515571795307, user=test, schema=db2, old schema=db2, borrowed=false, fromSlaveDB=false, threadId=23687,character_set_client=latin1,character_set_results=latin1,collation_connection=utf8_general_ci, txIsolation=3, autocommit=true, attachment=null, respHandler=null, host=10.186.23.67, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false]
2018-01-10 16:09:55.325  INFO [BusinessExecutor0] (com.actiontech.dble.backend.mysql.nio.MySQLConnectionHandler.closeNoHandler(MySQLConnectionHandler.java:195)) - no handler bind in this con com.actiontech.dble.backend.mysql.nio.MySQLConnectionHandler@3bf0a0ff client:MySQLConnection [id=4, lastTime=1515571795307, user=test, schema=db2, old schema=db2, borrowed=false, fromSlaveDB=false, threadId=23687,character_set_client=latin1,character_set_results=latin1,collation_connection=utf8_general_ci, txIsolation=3, autocommit=true, attachment=null, respHandler=null, host=10.186.23.67, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false]