File postgresql-README.SUSE of Package postgresql10.7543
Newer versions of PostgreSQL come with the pg_upgrade tool that simplifies and speeds up the migration of a PostgreSQL installation to a new version. Formerly dump and restore was needed that was much slower. pg_upgrade needs to have the server binaries of both versions available. To allow this, we had to change the way PostgreSQL is packaged as well as the naming of the packages, so that two or more versions of PostgreSQL can be installed in parallel. Starting with version 9.1, PostgreSQL package names contain numbers indicating the major version. In PostgreSQL terms the major version consists of the first two components of the version number, i.e. 8.3, 8.4, 9.0, or 9.1. So, the packages for Postgresql 9.1 are named postgresql91, postgresql91-server, etc. Inside the packages the files were moved from their standard locations to a versioned location such as /usr/lib/postgresql83/bin or /usr/lib/postgresql91/bin to avoid file conflicts if packages are installed in parallel. The update-alternatives mechanism creates and maintains symbolic links that cause one version (by default the highest installed version) to re-appear in the standard locations. By default, database data are stored under /var/lib/pgsql/data on SUSE Linux. The following preconditions have to be fulfilled before data migration can be started: 1. If not already done, the packages of the old PostgreSQL version must be upgraded to the new packaging scheme through a maintenance update. For SLE11 this means to install the patch that upgrades PostgreSQL from version 8.3.14 to 8.3.19 or higher. 2. The packages of the new PostgreSQL major version need to be installed. For SLE11 this means to install postgresql91-server and all the packages it depends on. As pg_upgrade is contained in postgresql91-contrib, that one has to be installed as well, at least until the migration is done. 3. Unless pg_upgrade is used in link mode, the server must have enough free disk space to temporarily hold a copy of the database files. If the database instance was installed in the default location, the needed space in megabytes can be determined by running the follwing command as root: "du -hs /var/lib/pgsql/data". If space is tight, it might help to run the "VACUUM FULL" SQL command on each database in the instance to be migrated, but be aware that it might take very long. Upstream documentation about pg_upgrade including step by step instructions for performing a database migration can be found under file:///usr/share/doc/packages/postgresql91/html/pgupgrade.html (if the postgresql91-docs package is installed), or online under http://www.postgresql.org/docs/9.1/static/pgupgrade.html . NOTE: The online documentation starts with explaining how you can install PostgreSQL from the upstream sources (which is not necessary on SLES) and also uses other directory names (/usr/local instead of the update-alternatives based path as described above). For background information about the inner workings of pg_admin and a performance comparison with the old dump and restore method, see http://momjian.us/main/writings/pgsql/pg_upgrade.pdf .
