MBS-13361: Upgrade the required version of PostgreSQL to 16

[mwiencek]

Problem

As explained in MBS-13361 and the schema change announcement blog post, we're requiring PostgreSQL 16 as of May 13.

Solution

Update our documentation and Docker test images to reference v16.

Testing

Ran the automated tests, plus have been using PostgreSQL v16 locally without issues for quite some time.

[reosarevok]

Tests pass - looking at https://www.postgresql.org/about/featurematrix/ I don't see any obvious places where we should refactor to use a much better new solution but you might, are there any?

[Kerollmops]

Suggested change

	if ($version < 160000) {
	if ($version < 16000) {

[reosarevok]

Surprised this didn't cause any issues with our tests, don't we test InitDb? Or is 160000 also valid, @mwiencek?

[mwiencek]

Thanks, I intended to leave a comment here but forgot. The previous check was incorrect; they increased the length of the number when their versioning system changed with major release 10. Here you can see what numbers are returned for v12, 15, and 16 respectively:

psql (12.16 (Ubuntu 12.16-1.pgdg22.04+1))
Type "help" for help.

musicbrainz_db=> SELECT current_setting('server_version_num');
 current_setting
-----------------
 120016
(1 row)

psql (15.6 (Homebrew), server 15.5 (Homebrew))
Type "help" for help.

musicbrainz_db=> SELECT current_setting('server_version_num');
 current_setting
-----------------
 150005
(1 row)

psql (16.1 (Debian 16.1-1.pgdg120+1))
Type "help" for help.

musicbrainz_json_dump=> SELECT current_setting('server_version_num');
 current_setting
-----------------
 160001
(1 row)

Surprised this didn't cause any issues with our tests, don't we test InitDb?

Yes, but we don't test this particular condition (nor multiple versions of PostgreSQL). Edit: To be clear, our tests hit this condition, but the check always fails; we don't test that it would pass with an older version of postgres.

[mwiencek]

Tests pass - looking at https://www.postgresql.org/about/featurematrix/ I don't see any obvious places where we should refactor to use a much better new solution but you might, are there any?

The one feature I saw as immediately useful is the new MERGE statement, but it would take some time to identify situations where we could make use of it. We certainly have many such cases though.