Shame on me for assuming, based on the explicit pg_dump command in the example.
This is what you wrote: >
> (Specifying the whole file name because multiple versions are installed.)
The path of the executable doesn't generally make a difference here
> $ /usr/lib/postgresql/12/bin/pg_dump --version
> pg_dump (PostgreSQL) 12.5 (Ubuntu 12.5-1.pgdg18.04+1)
Your 5432 database...
> postgres=# \d+ measu
rement
No idea how you got to this psql prompt, the last command you showed doesn't give you one. Not going to assume this isn't "one of the other of the multiple versions you have installed".
Then you show that your 5432 database has data.
> pg_dump -p 5433
Your dump of your 5433 database doesn't have data..
Typos or otherwise, the imprecise nature of your example drew attention to a possible typo-related problem, as opposed to the true "partitioned table" problem.
The fact that you didn't ask a better (more specific question), or otherwise state your expectations (which I presume would have pointed out the partitioned table dynamic) didn't help.
Sure, I could have been more careful in my reviewing of the posted material and made more of an effort to figure out what is correct, what is wrong, and what is confusing you. But this is also best-effort, and typos end up being the solution often enough that I don't usually dive deeper until that is ruled out (though here I did register the partitioned table aspect eventually).
David J.