In the last several months at Grazr, we've been wrestling with a large database (running on MySQL) of feeds and feed items. The schema is essentially a feeds table with child tables items, items_text (text), and enclosures. We have this database to provide the means for users to be able to merge (a Stream) feeds so that you have an aggregate feed with items for whatever feeds you want in the list of feeds for your merge. It works great, the only problem being the volume of data, which more data means the query to produce that merge becomes slower. We want this merge to be able to be run on the fly, and if it's too slow, the user experience is unacceptable.

So, now I'm in the process of implementing a "Hot Cache" of feeds with an LRU (Least Recently Used) policy. The idea being, that this cache provides a smaller data set for performing the merge query against. We need to be able to handle storing much more data than we currently do …