Cool analysis. I wonder if you could show something like a LOESS curve fitted across all the articles' timeseries? Or if they're all roughly linear descents, I wonder if you could show the distribution of slopes - do some descend faster than others? Why?<p>And then, a bone to pick:<p>Need a beefy RDBMS for 15mm rows? Maybe if you want to store the whole denormalized table in memory, but if you're just indexing a small field (or even partial-indexing a larger field) you should have no problem. The table will just spill to disk and page in as necessary, and you're mostly appending anyway so you shouldn't have much trouble. Plus, you could normalize the data: store the (large) article title in an Articles table with an id (hash of title?) and then just store the ranks in a Ranks table for <i>less</i> overall storage than the NoSQL database (thus needing a less-beefy machine).<p>Nothing against modern Not-only-SQL solutions or document stores, but don't discount RDBMS. Schemas aren't so scary or unwieldy that you should never use them.<p>Anyway, thanks for an informative post!