You&#x27;re probably thinking about this as &quot;instances of NoSQL services replacing RDBMS installations&quot; but that&#x27;s putting the playing field in the wrong place. Look at it as a venn diagram. There are 3 important zones: the zone where RDBMS excels; the zone where RDBMS and NoSQL compete and one or the other may be preferable depending on circumstances; and the zone where RDBMS never makes sense. You&#x27;re looking at the field as the first two zones, Yegge is looking at all three zones.<p>Which means that you&#x27;re missing things like caching engines, such as memcached, and other services which are not <i>replacing</i> an RDBMS but filling a different niche, which are widely deployed in industry.