My forum is under attack

[amfor]

I have a follow problem. Some user attack my forum by creating of multiple sessions. He created 2500 sessions per minute and vbullsession table is become full within a few minutes. In results the forum crashes.

MySQL Error : The table 'vbullsession' is full
Error Number : 1114
Request Date : Saturday, December 24th 2016 @ 07:03:25 AM
Error Date : Saturday, December 24th 2016 @ 07:03:25 AM

I block his IP's but he change it constantly (seems he uses different proxies). He attack forum in the night time when admins are out of forum and block access of members to forum on a whole night.

He do it a few last days.

Please help me to solve this problem. Maybe it's possible to limit quantity of sessions per one IP or something like this. It's very important.

Many thanks.