The PostgreSQL experiment turned out to not be as stellar as I had hoped. With our volume, the disk write load for bayes auto-learn is extremely high, even with fsync disabled, share mem increased, etc. I also ran into some severe concurrency issues - lots of waiting on locks, even with only one system doing updates and the others reading. Auto-vacuum set to 60 seconds (every 3 minutes for the SpamAssassin table) appears to help a tremendously. I think we'd need a solid state disk, or SAN with a large buffer, to safely handle it with a larger number of tokens. I'm also getting failed expires due to 'deadlock detected'.
Regrouping, I was looking at benchmarks for QDBM and see it is on the "we need volunteers" list. Is this more than just changing the "tie" in the Bayes DBM store module? Wes
