There are many reasons behind CouchDB not using Mnesia :
* It provides a storage limitation of 2 gigs per file.
* It requires validation and fixup cycle after a crash or power failure, so even if the size limitation is lifted, the fixup time on large files is prohibitive.
* Mnesia has some useful features, but features of Mnesia aren't really useful for CouchDB.
* Mnesia is not a general-purpose, large-scale database. It works best as a configuration type database.
* Mnesia works best as a configuration type database. It is necessary for the normal operations. The type where the data is not central to the function of the application, but necessary for normal operation of it.
* Things that need to update, configure and often reconfigure like a network router, HTTP proxies, etc. whose configuration data is rarely huge.
