Backstory: I had a debian 11 VPS. I installed the postgresql program from the debian 11 apt repo, back a few months ago. Back then, it was postgres 13 on the debian stable repos.

Fast forward couple months: debian 12 comes out. I do a “apt dist-upgrade” and in-place upgrade my VPS from debian 11 to debian 12. Along with this upgrade, comes postgresql 15 installed.

Now, fast forward couple more months: lemmy 0.18.3 comes out. I do not upgrade (I am on lemmy 0.18.2—afaik).

Fast forward some time, too: lemmy 0.18.4 comes out. I decide to upgrade to 0.18.4 from my existing 0.18.2.

I pull the git repo. Compile it locally. It goes well, no errors in the compilation process. I stop the lemmy systemd service, then I “mv” the compiled “lemmy_server” to /usr/bin dir.

I try to restart the now-upgraded lemmy systemd service. However, the systemd service fails.

I check the sudo journalctl -fu lemmy and I see the following error message:

lemmy_server[17631]: thread 'main' panicked at 'Couldn't run DB Migrations: Failed to run 2023-07-08-101154_fix_soft_delete_aggregates with: syntax error at or near "trigger"', crates/db_schema/src/utils.rs:221:25

I report this issue here: https://github.com/LemmyNet/lemmy/issues/3756#issuecomment-1686439103

However, after a few back and forths and internet search, I conclude that somewhere between lemmy 0.18.3 and 0.18.4, lemmy stops supporting psql <15. So, my existing DB is not compatible.

Upon my investigation on my VPS setup, I concluded that psql 15 is running, however, lemmy is using the psql 13 tables (I do not know if this is the correct term).

Now my question: is there a way to import the lemmy data I had in the psql 13 tables to a new psql 15 table (or database, I don’t know the term).

To make things hairier: I also run a dendrite server on the same VPS, and the dendrite server is using the psql 15 with psql 13 tables on the same database as the lemmy one.

The dendrite database is controlled by a psql user named “dendrite” and the lemmy database is controlled by a psql user named “lemmy” . I hope this makes differentiation between two databases possible. And so I do not harm my existing dendrite database.

Any recommendations about my options here?

        • Anark Karabey@monero.townOP
          2·
          1 year ago

          Speaking of, I think remove the environment variable from there, as it will take precedence.

          I will remove the following line we have added yesterday:

          Environment=LEMMY_DATABASE_URL=postgres://lemmy:REDACTED@127.0.0.1:5433/lemmy

          How do we transform this line so that it fits into the lemmy.hjson file?

            • Anark Karabey@monero.townOP
              2·
              1 year ago

              /etc/lemmy/lemmy.hjson file doesn’t have a port directive in it yet. We are going to add one now. And yes, the expected port number should be 5433, which is for postgresql 15.

              • RoundSparrow @ BT@bulletintree.comM
                2·
                1 year ago

                So to recap, should be easy for our next attempt:

                1. put the port in lemmy.json
                2. remove the environment variable from service file
                3. start attempt, see if it has your old data available
                4. If no old data, stop immediately

                I suppose for future, maybe worth some effort to block federation in the NGINX or something to make sure federation doesn’t kick off on wrong data if it isn’t what we expect

                • Anark Karabey@monero.townOP
                  2·
                  1 year ago
                  1. done
                  2. done
                  3. started lemmy.service — no errors, status shows active. I also started lemmy-ui.service — again, no errors, status shows active
                  4. my domain.tld on my tor browser (my usual browser) still shows a Setup Screen for a new Lemmy instance.

                  My suggestion: Although I have updated lemmy backend to the v0.18.4, I have not yet upgraded the lemmy-ui (frontend) to its latest version. Should I compile lemmy-ui again, so that we have its latest version, too, and then try again?

                  • RoundSparrow @ BT@bulletintree.comM
                    2·
                    1 year ago

                    yha, it is (lemmy-ui update) probably ok to do it since you are not in an urgent attempt to get online.

                    This isn’t what I expected… it isn’t talking to your PG13 that 0.18.2 had (or it would error) and it seems to be talking to the empty new database again.

                    Make sure you stop server. I think we need to pg_dumpall and try to make sense of this

          • RoundSparrow @ BT@bulletintree.comM
            1·
            1 year ago

            How do we transform this line so that it fits into the lemmy.hjson file?

            We don’t… your lemmy.hjson you were using for 0.18.2 - if you used the same password, the only thing we need to do is add the port to 5433… the URL doesn’t need to go into that file

            • Anark Karabey@monero.townOP
              2·
              1 year ago

              if you used the same password

              Yes, I used the same psql password.

              OK. Then, I am going to remove the

              Environment=LEMMY_DATABASE_URL=postgres://lemmy:REDACTED@127.0.0.1:5433/lemmy

              line from the lemmy.service file. And then, I will add the port directive.

              The updated /etc/lemmy/lemmy.hjson file is as follows now:

              {
  database: {
    # put your db-passwd from above
    password: "REDACTED"
    port: 5433
  }
  # replace with your domain
  hostname: domain.tld
  bind: "127.0.0.1"
  federation: {
    enabled: true
  }
  # remove this block if you don't require image hosting
  pictrs: {
    url: "http://localhost:8080/"
  }
}

              observe that I have added the port: 5433 to the database: clause.