Do you know how to avoid the following fatal error message :
"...MySQL server has gone away".
I suppose this means that PDO connection to MySQL has been lost.
I have checked MySQL max_allowed_packet
variable which is equal to 268435456 (I think this value is more than enough).
Thanks for your respective answers. After few days of investigations, I decided to reset PDO MySQL connection every 250 seconds. I know it is not the best in class solution but it is at least a solution to avoid the problem.