[ssmoot]

An IdentityMap would resolve the issue with your second-layer cache, allowing you to select only the columns necessary, which can be a very significant win.

Ruby O/RMs for example generally take a big hit from loading date/time-columns. If you don't need the columns most of the time, then why load them?

Many (not all) databases will take a significant hit when loading TEXT columns. Again, most of the time you probably don't need them, and could be better served with a 'summary' column.

Just nit-picking really. Though I do generally try to think of caching as a last resort; too often it feels like a hammer for compromised design.