How do you list all items from all databases located in a specific tablespace in postgresql?
pg_tables seems to be db-specific, whereas (I think) tablespaces are global for a postgres instance.


That's true. But there is no way of knowing what's inside of a tablespace without connecting to the specific databases and checking their catalogs. Iterating is the only option. Think of it like a glorified virtual storage system.

You may consider running pg_dumpall --schema-only and trying to parse that output if you're interested.