On 24 Mar 2009, at 15:02, Brian Stansberry wrote:

1. Drop MRU and LFU. I don't see MRU being useful except in very specific edge cases. LRU somewhat useful but very expensive.

Did you mean "LFU somewhat useful"? If so, yeah, agreed.

Yes, LFU.

2. Re-introduce a time-based watermark. Brian, this is where your thoughts are most useful - how do you see this being used? In passivation?

Theoretically it's important for passivation, but in practice I find it makes more sense to let the web/sfsb container decide what gets passivated. So don't let AS passivation drive this.

For entity caching, supporting maxAge is very important as that allows guaranteed flushing of stale data from the cache; important in use cases where other systems may update the DB making the cache invalid, but the application is willing to accept that for a certain period.

Right. I have this in the form of lifespans, which can be set either cache-wide or per-entry.

Eviction based on time-since-last-access I think is more of a convenience. It helps shield users from needing to think about # of nodes; they can just reason "if this data hasn't been used in 5 minutes, I don't need it." A nice heuristic.

With the flat structure the problem of reasoning about number of nodes is a bit less, since structural nodes are gone.

My gut feeling on this is that eviction based on time-since-last-access is not strictly necessary but if you take it away you'll get lots of grumbling.

I've found a way to introduce it easily enough with minimal impact/cost. It would sit alongside lifespan, as a maxIdle time.