The article you linked disagrees - they said it pretty well:
Of course, some issues come from the fact that people are trying to use the Relational model where it doesn’t suit their use case. That’s why I prefer a document model instead of a tabular one as the default choice. Most of our applications are more suitable for it, as we’re still moving the regular physical world (so documents) into computers. (Read also more in General strategy for migrating relational data to document-based).
I never joined the NOSQL hype-train so I can’t comment on that. However I will point out storing documents on a disk is a very well established and proven approach… and it’s even how relational databases work under the hood. They generally persist data on the filesystem as documents.
Where I find relational data really falls over is at the conversion point between relational document representation. That typically happens multiple times in a single operation - for example when I hit the reply button on this comment (I assume, haven’t read the source code) this is what will happen:
my reply will be sent to the server as a document, in body of a HTTP request
beehaw’s server will convert that document into relational data (with a considerable performance penalty and large surface are for bugs)
PostgreSQL is going to convert that relational data back into a document format and write it to the filesystem (more performance issues, more opportunities for bugs)
And every time the comment is loaded (or sent to other servers in the fediverse) that silly “document to relational to document” translation process is repeated over and over and over.
I’d argue it’s better, more efficient, to just store this comment as a document because over and over and over it’s going to be needed in that format and anyway you ultimately need to write it to disk as a document.
Yes - you should also have a relational index containing critical metadata in the document. The relationship linking that document to the comment that I replied to. The number of upvotes it has received. Etc Etc… but that should be a secondary database, not the primary one. Things like an individual upvote should also be a document, stored as a file on disk (in the format specified by AcitivtyStreams 2.0).