Milter-greylist

Hello everyone,

I am currently running the 3.0 build of milter-greylist (previously running various 3.0rc# releases), and continue to have a problem with sync'ing.  We have 4 servers, all handling about 500,000 messages total daily.

Peer sync'ing will work for a period of time, then start producing "peer queue overflow" errors.  This happens on different servers at different times.  What we've noticed is that the error will affect a particular server, but the other servers will continue to sync with each other with no problem; so the problem appears to be localized to the server initiating the synchronization.  (And eventually, all the servers will end up with queue overflow errors.)

In addition, the affected server appears to no longer successfully synchronize *any* information, and only killing the milter process and restarting it, does synchronization work again.  The TCP connection remains established the whole time, so I can't see any connectivity problem between the affected server and its peers.  We don't see any other bottlenecks on the system, and the rest of the local milter-greylist functionality continues to work during these sync failures.  We've even tried increasing the value of SYNC_MAXQLEN in sync.h to 10240, and the problem still occurs.

My questions are:  What are some potential causes of "peer queue overflow" errors?  What is the expected behavior in the event of an overflow -- should at least *some* records continue to be synchronized (while dropping others)?  Why would one server register a peer queue overflow for *all* other peers, when each of those peers can receive sync'd information just fine from their other peers -- unless there is a problem specific to the server initiating the sync?

Thanks to anyone who can help or offer any information,
Patrick