delayed update on sql logging

Hi, I am checking simultaneous-use information, logged users etc on sql server. The problem is, if a user logges in, nearly after a minute later i can see the logged on user on mysql tables. But i can see the same user with radlast command in the same second the user logs in. So it seems like there is a delay between updating the data on sql. And with this, user can log in mutliple times with same username even i set sim-use to 1. Is there any parameter for that??? Or what else can cause that problem.