Update database README.

Add information on restoring from backup and troubleshooting
details when migrating PostgreSQL versions.

etc/db/README.md

@@ -76,6 +76,17 @@ sudo -u postgres /usr/lib/postgresql14/bin/pg_upgrade --link \
   --old-datadir="/srv/pgsql/data/" \
   --new-datadir="/srv/pgsql/data14/"
 
+# NOTE: If getting the following error:
+# lc_collate values for database "postgres" do not match:  old "en_US.UTF-8", new "C"
+# then:
+# cd ..
+# rm -rf /srv/pgsql/data14
+# install -d -m 0700 -o postgres -g postgres /srv/pgsql/data14
+# cd /srv/pgsql/data14
+# sudo -u postgres /usr/lib/postgresql14/bin/initdb --locale=en_US.UTF-8 .
+#
+# and repeat the migration command
+
 # After successfully migrating the data...
 cd ..
 # if not already symlinked move the old data to a versioned directory matching
@@ -95,3 +106,34 @@ systemctl start postgresql.service
 # For good measure:
 sudo -u postgres /usr/lib/postgresql14/bin/vacuumdb --all --analyze-in-stages
 ```
+
+# Restoring from backup
+
+## Whole database
+
+Ensure that nothing is connected to the database.
+
+```bash
+psql -U postgres --dbname postgres <<EOF
+-- Database: dougal
+
+DROP DATABASE IF EXISTS dougal;
+
+CREATE DATABASE dougal
+    WITH
+    OWNER = postgres
+    ENCODING = 'UTF8'
+    LC_COLLATE = 'en_GB.UTF-8'
+    LC_CTYPE = 'en_GB.UTF-8'
+    TABLESPACE = pg_default
+    CONNECTION LIMIT = -1;
+
+ALTER DATABASE dougal
+    SET search_path TO "$user", public, topology;
+
+EOF
+
+# Adjust --jobs according to host machine
+pg_restore -U postgres --dbname dougal --clean --if-exists --jobs 32 /path/to/backup
+
+```