Milter-greylist

I am getting these constantly on my mailscanners

Oct 17 08:11:07 mailscannerx milter-greylist: peer 70.x.x.x queue 
overflow (1024 entries), discarding new entry
Oct 17 08:11:07 mailscannerx milter-greylist: peer 70.x.x.x queue 
overflow (1024 entries), discarding new entry
Oct 17 08:11:07 mailscannerx milter-greylist: peer 70.x.x.x queue 
overflow (1024 entries), discarding new entry


I x'd out the ips but you get the idea.  Everything will be going great 
and then all of a suddent I'll get these errors.  If I do a 'service 
miltergrey restart' it will start working again.  Why is the queue 
overflowing?  Is 1024 entries max for a 10 minute interval or 
something?  Can I increase this number?  My servers handle 300-500K 
messages daily so the greylist.db could be quite large, right now its 
20 megs.