I have some INSERT/UPDATE queries who takes a long time randomly.
I try to launch the same INSERT several times with profiling enable.

And I remark that the duration is always in waiting for handler commit.

starting | 0.000186  
Executing hook on transaction | 0.000006  
starting | 0.000007  
checking permissions | 0.000006  
Opening tables | 0.000083  
init | 0.000007  
System lock | 0.000010  
update | 0.000142  
end | 0.000005  
query end | 0.000003  
waiting for handler commit | 0.402701  
closing tables | 0.000054  
freeing items | 0.000123  
cleaning up | 0.000038  

I execute only my INSERT query, no other queries are executed at the same time.

I have 16GB RAM, my innodb_buffer_pool_size is set to 8G.

I try to set several values to innodb_buffer_pool_size but it doesn’t work better.