Database growing

Hi everybody, sorry for my english,

I backup often my database and see how it’s growing (823Mo this night), i read about deleting logs but i’m afraid to do this because i do not want to loose data. piwik_log_link_visit_action make 227Mo, but if i understand it well, it’s the memory of each visit so i need to keep it. I not understand the help panel talking about deleting the log tables.

Someone can help me to understand ?
I have an up to date simple basic installed Piwik.

Maybe i have to do nothing :s

Thanks in advance,