performance issue with g2_SessionMap

Today my site was shutdowned by bluehost because of the slow mysql query. After checking, I found that it's because of the DELETE operation on g2_SessionMap.

# Thu May 15 00:31:02 2008
# Query_time: 213 Lock_time: 0 Rows_sent: 0 Rows_examined: 0
use gallery2;
DELETE FROM g2_SessionMap
WHERE g2_SessionMap.g_creationTimestamp < 1209018449
OR g2_SessionMap.g_modificationTimestamp < 1210228049 OR
(g2_SessionMap.g_userId = 5 AND g2_SessionMap.g_creationTimestamp < 1210228049)
LIMIT 500

Anyone knows what is this for and how could I avoid this operation from my site so that my site won't be shutdown again.
Is it possible not to use the g2_SessionMap table anymore?

Thanks a lot!