I'm a bit surprised. Postgres is one of the possible database you can use on XWiki, which is something quite comparable to Confluence. Postgres seems to do fine and relational databases have strengths that are not to be discarded too early.
Confluence itself uses relational databases including Postgres, and they seem to do well too.
And I know for a fact that both handle huge wikis. (hundreds of spaces, millions of document revisions)
I’m by no means suggesting they abandon RDBMS, just that they shift large textual / binary content out of it, and store pointers instead.
You can store essentially anything in an RDBMS, especially Postgres. That doesn’t make it the right choice. It might make it easier, but easier isn’t the same thing as correct.
I am of course biased as a DBRE, since I’m the one who gets paged about problems caused by decisions like this. Then I get to deliver the uncomfortable news that everything needs to be overhauled, and inevitably am told that’s not going to happen, and to just figure it out.
Confluence itself uses relational databases including Postgres, and they seem to do well too.
And I know for a fact that both handle huge wikis. (hundreds of spaces, millions of document revisions)