(In reply to haidong li from comment #0)
> Description of problem:
> seq_num in table Controller_Event doesn't increase when receive more
> empty_lb_backends packets
> 
> Version-Release number of selected component (if applicable):
> [root@dell-per730-19 opt]# uname -a
> Linux dell-per730-19.rhts.eng.pek2.redhat.com 3.10.0-1061.el7.x86_64 #1 SMP
> Thu Jul 11 21:02:44 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
> [root@dell-per730-19 opt]# rpm -qa | grep openvswitch
> openvswitch-selinux-extra-policy-1.0-13.el7fdp.noarch
> openvswitch2.11-2.11.0-18.el7fdp.x86_64
> [root@dell-per730-19 opt]# rpm -qa | grep ovn
> ovn2.11-central-2.11.0-26.el7fdp.x86_64
> ovn2.11-2.11.0-26.el7fdp.x86_64
> ovn2.11-host-2.11.0-26.el7fdp.x86_64
> [root@dell-per730-19 opt]#
> 
> How reproducible:
> everytime
> 
> Steps to Reproduce:
> 1.add logical switch and add empty_lb_backends load_banlancer to it
> 2.send tcp packets to vip,the Controller_Event is created and seq_num is 1
> 3.send tcp packets again,the seq_num doen't increase
> 
> Actual results:
> [root@dell-per730-19 opt]# ovn-nbctl list load_balancer
> _uuid               : 0d3a7dcc-a162-4f9c-a2cd-8a1eec113ee0
> external_ids        : {}
> name                : "lb0"
> protocol            : tcp
> vips                : {"172.16.13.100"="", "172.16.13.100:80"="",
> "172.16.13.200"="", "172.16.13.200:80"=""}
> 
> [root@dell-per730-19 opt]# 
> [root@dell-per730-19 opt]# ovn-nbctl ls-lb-list s2 
> UUID                                    LB                  PROTO      VIP  
> IPs
> 0d3a7dcc-a162-4f9c-a2cd-8a1eec113ee0    lb0                 tcp/udp   
> 172.16.13.100       
>                                                             tcp       
> 172.16.13.100:80    
>                                                             tcp/udp   
> 172.16.13.200       
>                                                             tcp       
> 172.16.13.200:80    
> 
> send packets:
> [root@localhost ~]# nc 172.16.13.100 80   < 2.txt
> 
> [root@dell-per730-19 opt]# ovn-sbctl list controller_even
> _uuid               : 70943ca3-8de2-4afb-98d6-7ed208835836
> chassis             : f704b2a1-0435-4627-9119-062cd3a5bba9
> event_info          : {load_balancer="0d3a7dcc-a162-4f9c-a2cd-8a1eec113ee0",
> protocol=tcp, vip="172.16.13.100:80"}
> event_type          : empty_lb_backends
> seq_num             : 1
> 
> Expected results:
> the seq_num can increase
> 
> Additional info:
> If remove the table and send packets again,the seq_num can increase
> 
> [root@dell-per730-19 opt]# ovn-sbctl destroy controller_even
> 70943ca3-8de2-4afb-98d6-7ed208835836
> [root@dell-per730-19 opt]# ovn-sbctl list controller_even
> 
> send packets:
> [root@localhost ~]# nc 172.16.13.100 80   < 2.txt
> 
> [root@dell-per730-19 opt]# ovn-sbctl list controller_even
> _uuid               : 921b71d6-8c1d-4e7f-977b-281535222b3f
> chassis             : f704b2a1-0435-4627-9119-062cd3a5bba9
> event_info          : {load_balancer="0d3a7dcc-a162-4f9c-a2cd-8a1eec113ee0",
> protocol=tcp, vip="172.16.13.100:80"}
> event_type          : empty_lb_backends
> seq_num             : 2

the seq_num field is updated just when the event is written in the controller_event table and not if ovn-controller receives a new event before the CMS has consumed the raw in the db.
Seq_num is used by the CMS to distinguish between two duplicated events reported by ovn-controller