At the inception of the web, SQL was NOT as well used as some would have us believe. One billion dollar company had only 1 SQL database for a minor support application, everything else was run on the AS/400 native file system, where everything including the file system is a database. So, if you sell a billion dollars worth of goods through a 300 location discount store operation, and *every* item is a line item entry taken from point of sale reporting boxes, that’s a *lot* of inserts. No way was SQL ever going to handle this volume in a 5 hour processing window.

The original Twitter complaint was that scaling the DB tier is difficult with Rails OOTB, not whether or not it should use a DB. I am still stunned by this suggestion for a site which is getting 11000 hits per second and even more discouraged by the number of people who think using files and filesystem in the manner described is a viable architecture option - let alone an alternative - for a Twitterlike site.