[Zope] when to opt for a backend DB over ZClasses?

I've done a number of smallish Zope sites that make heavy use of ZClasses and ZCatalogs. Now I'm involved with a project where we need to create (and search over) millions of objects. Even though the objects are relatively lightweight (just a few floats and strings), should we be using a backend database rather than ZClasses? This comes up a lot in the archives, but I've never seen a clear exposition of when one should forego the beauty of ZClasses for a more traditional (backend) storage. Cheers, Darran. --------------------------------------------- This message was sent using Endymion MailMan. http://www.endymion.com/products/mailman/