Update database README.

Document how to create a Dougal database from scratch
and how to update PostgreSQL.

etc/db/README.md

@@ -19,3 +19,79 @@ Created with:
 ```bash
 SCHEMA_NAME=survey_X EPSG_CODE=XXXXX $DOUGAL_ROOT/sbin/dump_schema.sh
 ```
+
+## To create a new Dougal database
+
+Ensure that the following packages are installed:
+
+* `postgresql*-postgis-utils`
+* `postgresql*-postgis`
+* `postgresql*-contrib` # For B-trees
+
+```bash
+psql -U postgres <./database-template.sql
+```
+
+---
+
+# Upgrading PostgreSQL
+
+The following is based on https://en.opensuse.org/SDB:PostgreSQL#Upgrading_major_PostgreSQL_version
+
+```bash
+# The following bash code should be checked and executed
+# line for line whenever you do an upgrade. The example
+# shows the upgrade process from an original installation
+# of version 12 up to version 14.
+
+# install the new server as well as the required postgresql-contrib packages:
+zypper in postgresql14-server postgresql14-contrib postgresql12-contrib
+
+# If not yet done, copy the configuration create a new PostgreSQL configuration directory...
+mkdir /etc/postgresql
+# and copy the original file to this global directory
+cd /srv/pgsql/data
+for i in  pg_hba.conf pg_ident.conf postgresql.conf postgresql.auto.conf ; do cp -a $i /etc/postgresql/$i ; done
+
+# Now create a new data-directory and initialize it for usage with the new server
+install -d -m 0700 -o postgres -g postgres /srv/pgsql/data14
+cd /srv/pgsql/data14
+sudo -u postgres /usr/lib/postgresql14/bin/initdb .
+
+# replace the newly generated files by a symlink to the global files.
+# After doing so, you may check the difference of the created backup files and
+# the files from the former installation
+for i in  pg_hba.conf pg_ident.conf postgresql.conf postgresql.auto.conf ; do old $i ; ln -s /etc/postgresql/$i .; done
+
+# Copy over special thesaurus files if some exists.
+#cp -a /usr/share/postgresql12/tsearch_data/my_thesaurus_german.ths /usr/share/postgresql14/tsearch_data/
+
+# Now it's time to disable the service...
+systemctl stop postgresql.service
+
+# And to start the migration. Please ensure, the directories fit to your upgrade path
+sudo -u postgres /usr/lib/postgresql14/bin/pg_upgrade --link \
+  --old-bindir="/usr/lib/postgresql12/bin" \
+  --new-bindir="/usr/lib/postgresql14/bin" \
+  --old-datadir="/srv/pgsql/data/" \
+  --new-datadir="/srv/pgsql/data14/"
+
+# After successfully migrating the data...
+cd ..
+# if not already symlinked move the old data to a versioned directory matching
+# your old installation...
+mv data data12
+# and set a symlink to the new data directory
+ln -sf data14/ data
+
+# Now start the new service
+systemctl start postgresql.service
+
+# If everything has been sucessful, you should uninstall old packages...
+#zypper rm -u postgresql12 postgresql13
+# and remove old data directories
+#rm -rf /srv/pgsql/data_OLD_POSTGRES_VERSION_NUMBER
+
+# For good measure:
+sudo -u postgres /usr/lib/postgresql14/bin/vacuumdb --all --analyze-in-stages
+```