if mysql cannot login for: ERROR 1129 (HY000): Host 'xx.xx.xx.xx' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts', dble cannot start up

[irene-coming]

version:5.6.29-dble-2.18.02.1-dev-20180428023831

[irene-coming]

Host 'host_name' is blocked info:
https://dev.mysql.com/doc/refman/8.0/en/blocked-host.html

a possible way to repeat the err:
(ps: 10.186.30.93 is dble resides host, mysql and dble installed in different servers)
step1:
login the mysqld and execute:
set global max_connect_errors=1;

step2, in mysql host do:
[root@zhj]# tc qdisc add dev eth0 handle 1: root prio
[root@zhj]# tc qdisc add dev eth0 handle 70: parent 1:3 netem loss 90%
[root@zhj]# tc filter add dev eth0 protocol ip parent 1: prio 2 u32 match ip dst 10.186.30.93 flowid 1:3

step3:
from 10.186.30.93 create a mysql connection to mysqld ( 10% chance need retry this step for netem loss 90%)
then get:
mysql: [Warning] Using a password on the command line interface can be insecure.
ctrl+c quit the login before you get:(wait about 1min with net.ipv4.tcp_syn_retries = 6)
ERROR 2003 (HY000): Can't connect to MySQL server on '10.186.30.86' (110)

step4, in mysql host do:
[root@zhj]# tc filter del dev eth0 protocol ip parent 1: prio 2 u32 match ip dst 10.186.30.93 flowid 1:3
[root@zhj]# tc qdisc del dev eth0 handle 70: parent 1:3 netem loss 90%
[root@zhj]# tc qdisc del dev eth0 handle 1: root prio

step5:
login the mysqld from '10.186.30.93' and get:
ERROR 1129 (HY000): Host '10.186.30.93' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'

if the block err does not occur, retry step2~step5

[yanhuqing666]

commit: 0c2eb61 and 1b5c502