That largely depends on the usage patterns of the app in question. Write operations can be particularly expensive, read operations much less so, especially wit

That largely depends on the usage patterns of the app in question. Write operations can be particularly expensive, read operations much less so, especially with application-level caching. Even as for write operations or notoriously expensive read operations such as full table scans modern RDBMS are optimised to a degree that for most applications database performance shouldn't be an issue. While traditional hard drives competed with the network for the title of "system component with the lowest bandwidth" (see http://www.cs.cornell.edu/projects/ladis2009/talks/dean-keynote-ladis2009.pdf http://www.cs.cornell.edu/projects/ladis2009/talks/dean-keyn...) accessing data on an SSD is way faster than accessing a resource via network. So, today the technical bottleneck (as in "component with the lowest bandwidth") in a typical web app system architecture is the network.