Deadlock happens when sink to mysql

[徐涛]

Hi Experts,
        I use the following sql, and sink to mysql, 
            select
    album_id, date
    count(1)
from
    coupon_5_discount_date_conv
group by
    album_id, date;

        when sink to mysql, the following SQL is executed: insert into xxx 
(c1,c2,c3) values (?,?,?) on duplicate key update c1=VALUES(c1),c2=VALUES(c2), 
c3=VALUES(c3)
        The engine is InnoDB, column c1,c2 is unique key, the isolation level 
is READ COMMITTED. But in the log a deadlock exception happens.
        As I know, because the unique key exists, only the line lock will be 
applied, no gap lock will be applied. And due to a group by sentence, the same 
unique key should be written by the same thread. So in this case, why the dead 
lock should happened? Could anyone help me? Thanks a lot.
        

Best
Henry