postgres: Allow specifying locale per-machine

Synapse needs the database to be in C locale. Since v1.56.0, it refuses
to start when this is not the case, see [upgrade.md][1].

Replace `en_US.UTF-8` with a variable where present and adapt the
`upgrade_pg.sh` script to copy the locale from the old cluster.

[1]: https://github.com/matrix-org/synapse/blob/c1482a352acd35055db93f5d0b5de1bec8974fa0/docs/upgrade.md#upgrading-to-v1560

playbooks/matrix.archlinux.org.yml

@@ -17,6 +17,7 @@
       postgres_work_mem: 64MB
       postgres_maintenance_work_mem: 256MB
       postgres_effective_cache_size: 4GB
+      postgres_locale: C
     - { role: postfix_null }
     - { role: matrix }
     - { role: fail2ban }

roles/postgres/defaults/main.yml

@@ -21,3 +21,5 @@ postgres_ssl_hosts4: []
 postgres_ssl_hosts6: []
 
 postgres_backup_dir: '/root/backup-postgres'
+
+postgres_locale: 'en_US.UTF-8'

roles/postgres/files/upgrade_pg.sh

@@ -30,6 +30,9 @@ if [[ -d /var/lib/postgres/data-$FROM_VERSION ]]; then
 	exit 3
 fi
 
+## Copy the locale from the old cluster
+locale=$(sudo -u postgres psql -A -t --dbname=template1 -c 'SHOW lc_collate;')
+
 # mask postgresql.service to make sure that other services with
 # Wants=postgresql.service and Restart=on-failure will not start
 # it again during the upgrade
@@ -42,7 +45,7 @@ chown postgres:postgres /var/lib/postgres/
 su - postgres -c "mv /var/lib/postgres/data /var/lib/postgres/data-$FROM_VERSION"
 su - postgres -c 'mkdir /var/lib/postgres/data'
 su - postgres -c 'chattr -f +C /var/lib/postgres/data' || :
-su - postgres -c 'initdb --locale en_US.UTF-8 -E UTF8 -D /var/lib/postgres/data'
+su - postgres -c "initdb --locale=$locale -E UTF8 -D /var/lib/postgres/data"
 vimdiff /var/lib/postgres/{data,data-$FROM_VERSION}/pg_hba.conf
 vimdiff /var/lib/postgres/{data,data-$FROM_VERSION}/postgresql.conf
 

roles/postgres/tasks/main.yml

@@ -23,7 +23,7 @@
   become: true
   become_user: postgres
   become_method: su
-  command: initdb --locale en_US.UTF-8 -E UTF8 -D '/var/lib/postgres/data'
+  command: initdb --locale={{ postgres_locale }} -E UTF8 -D '/var/lib/postgres/data'
   args:
     chdir: /var/lib/postgres
     creates: /var/lib/postgres/data/postgresql.conf

roles/postgres/templates/postgresql.conf.j2

@@ -691,11 +691,11 @@ timezone = 'UTC'
 					# encoding
 
 # These settings are initialized by initdb, but they can be changed.
-lc_messages = 'en_US.UTF-8'			# locale for system error message
+lc_messages = '{{ postgres_locale }}'			# locale for system error message
 					# strings
-lc_monetary = 'en_US.UTF-8'			# locale for monetary formatting
-lc_numeric = 'en_US.UTF-8'			# locale for number formatting
-lc_time = 'en_US.UTF-8'				# locale for time formatting
+lc_monetary = '{{ postgres_locale }}'			# locale for monetary formatting
+lc_numeric = '{{ postgres_locale }}'			# locale for number formatting
+lc_time = '{{ postgres_locale }}'				# locale for time formatting
 
 # default configuration for text search
 default_text_search_config = 'pg_catalog.english'