One of the ways to upgrade a PostgreSQL database from one server version to
another is to use the built-in pg_upgrade command. This can be faster and
require fewer manual steps than something like a pg_dump and pg_restore.
However, before you run the pg_upgrade command for real, you should check
that the target database is compatible with the current database. To do this,
write your pg_update command with all the flags you need and then tack on
--check at the end. This does a dry-run reporting the results of a series of
consistency checks.
Here is what a successful check looks like:
$ /usr/local/opt/postgresql@13/bin/pg_upgrade \
--old-bindir $HOME/.asdf/installs/postgres/12.3/bin \
--new-bindir /usr/local/opt/postgresql@13/bin \
--old-datadir $HOME/.asdf/installs/postgres/12.3/data \
--new-datadir ./postgres/data \
--check
Performing Consistency Checks
-----------------------------
Checking cluster versions ok
Checking database user is the install user ok
Checking database connection settings ok
Checking for prepared transactions ok
Checking for system-defined composite types in user tables ok
Checking for reg* data types in user tables ok
Checking for contrib/isn with bigint-passing mismatch ok
Checking for presence of required libraries ok
Checking database user is the install user ok
Checking for prepared transactions ok
Checking for new cluster tablespace directories ok
*Clusters are compatible*If there is an issue, such as mismatched collation settings, the output will report the issue. You'll have to decide how to resolve those on a case-by-case basis.