Assume I have an older major PostgreSQL version (f.e. 15.4) already uninstalled and only the data folder left behind. Can I import that data folder into a newer major version (f.e. 16.3) with only the newer version being installed? If so, how?
For minor versions (f.e. 16.1 -> 16.3) it is possible to simply use the same data folder. (according to the documentation here)
For major versions the "traditional method for moving data to a new major version is to dump and restore the database" (according to the same docu link). It also says that "it is recommended that you use the pg_dump and pg_dumpall programs from the newer version of PostgreSQL", but how can I call pg_dumpall on the old data folder to create a dump that I can import into the new installed version? With the -d or -l parameters? Or would the PostgreSQL server instance first have to point to the old data folder (which I assume does not always work) before I can use pg_dumpall on it?
The other recommended option is pg_upgrade, but it seems to require the old PostgreSQL executable directory (-oldbindir parameter), so I assume I cannot use that tool with only the newer major version installed.
The data files of PostgreSQL major version are not compatible. To use your PG15 data in a version 16 server you'll need to re-install version 15, start a postgres-15 server with the old data directory and either:
It is recommended that you use the pg_dump and pg_dumpall programs from the newer version of PostgreSQL, to take advantage of enhancements that might have been made in these programs. Current releases of the dump programs can read data from any server version back to 9.2.