Now the log table structure is:
log_time, action, user_id, ip, tablename

the action is like: add record 1

I have a suggestion to midify the structure to be:
log_time, action, user_id, ip, tablename, record, memo

the action filed is only a action type: add, del, mod, loginout
the record field is the record ID of the action

I wish the setup of table have an option: whether record the record change detail. If yes, when modify a record, system can compare every field of after and befor the modify, then record the original content of changed field. It will be very useful to trace the change.