PostgreSQL 12 was released on 2019-10-03. You can upgrade from an older version either with pg_dumpall or with pg_upgrade. The variant described below uses pg_upgrade.

Install PostgreSQL 12

sudo apt-get update
sudo apt-get install postgresql-12 postgresql-server-dev-12

Move your custom settings from the old configs into the new ones. It’s convenient to review the differences between the configs of the two versions with:

diff /etc/postgresql/11/main/postgresql.conf /etc/postgresql/12/main/postgresql.conf
diff /etc/postgresql/11/main/pg_hba.conf /etc/postgresql/12/main/pg_hba.conf

Stop the running PostgreSQL

sudo systemctl stop postgresql.service

Switch to the directory for temporary files. Logs will be written there and some scripts will be added:

cd /tmp

Start working on the command line as the postgres user:

sudo su postgres

Check the clusters

Safely check the clusters, without modifying any data:

/usr/lib/postgresql/12/bin/pg_upgrade \
  --old-datadir=/var/lib/postgresql/11/main \
  --new-datadir=/var/lib/postgresql/12/main \
  --old-bindir=/usr/lib/postgresql/11/bin \
  --new-bindir=/usr/lib/postgresql/12/bin \
  --old-options '-c config_file=/etc/postgresql/11/main/postgresql.conf' \
  --new-options '-c config_file=/etc/postgresql/12/main/postgresql.conf' \
  --check

Migrate the data

If there are no errors, perform the data migration (if you don’t need to copy the files into the new cluster, use the --link parameter — hard links to the old cluster will be used, without copying):

/usr/lib/postgresql/12/bin/pg_upgrade \
  --old-datadir=/var/lib/postgresql/11/main \
  --new-datadir=/var/lib/postgresql/12/main \
  --old-bindir=/usr/lib/postgresql/11/bin \
  --new-bindir=/usr/lib/postgresql/12/bin \
  --old-options '-c config_file=/etc/postgresql/11/main/postgresql.conf' \
  --new-options '-c config_file=/etc/postgresql/12/main/postgresql.conf'

Return to your regular user:

exit

Swap the ports

Your old PostgreSQL most likely used port 5432, while the new one uses port 5433 by default. Swap them.

sudo vim /etc/postgresql/12/main/postgresql.conf
# change "port = 5433" to "port = 5432"

sudo vim /etc/postgresql/11/main/postgresql.conf
# change "port = 5432" to "port = 5433"

Start PostgreSQL

sudo systemctl start postgresql.service

Work as the postgres user:

sudo su postgres

Check the version of the running PostgreSQL:

psql -c "SELECT version();"

The new cluster has no statistics yet. You need to run ANALYZE over the cluster. For this, pg_upgrade created the script analyze_new_cluster.sh. Run it.

./analyze_new_cluster.sh

Return to your regular user:

exit

Remove the old version

See which old PostgreSQL versions remain in the system.

apt list --installed | grep postgresql

Remove the old PostgreSQL versions, for example:

sudo apt-get remove postgresql-11

Remove the old configuration:

sudo rm -rf /etc/postgresql/11/

Log in as the postgres user one last time:

sudo su postgres

Delete the old cluster’s data:

./delete_old_cluster.sh

The upgrade is complete!