Well, it worked for Amazon — Berkeley DB was used extensively there as the makn database, right from the beginning. I remember talking to an ex-Amazon engineer in 2006 who said BDB was still the main database used for inventory, and complained that everything was a mess, with different teams using different tech for everything. Around that time Amazon made DynamoDB to solve some of that mess — and it sat on top of BDB.
An old thread about this: https://news.ycombinator.com/item?id=29290095.
Can verify. When I started in the catalog department in '97, "the catalog" was essentially a giant Berkeley DB keyed on ISBN/ASIN that was built/updated and pushed out (via a mountain of Perl tools) to every web server in the fleet on a regular cadence. There were a bunch of other DBs too, like for indexes, product reviews, and other site features. Once the files landed, the deploy tooling would "flip the symlinks" to make them live.
Berkeley DBs were the go-to online databases for a long time at Amazon, at least until I left at the turn of the century. We had Oracle databases too, but they weren't used in production, they were just another source of truth for the BDBs.
It worked well for Amazon because they kept it within a tight operating envelope. They used it to persist bytes on disk in multiple, smaller BDBs per node. This kept it out of trouble. They also sidestepped the concurrency and locking problems by taking care of that in the layers above. It was used more like SSTables in BigTable.
They phased out BDB before DynamoDB was launched. Some time between 2007 and 2010. By the time DynamoDB launched as a product in 2012(?), BDB was gone.