forked from pool/postgresql12
81 lines
3.8 KiB
Plaintext
81 lines
3.8 KiB
Plaintext
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Unix-Domain Socket Directory
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============================
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Upgrading PostgreSQL on openSUSE and SUSE Linux Enterprise Server
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=================================================================
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Current versions of PostgreSQL come with the pg_upgrade tool that
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simplifies and speeds up the migration of a PostgreSQL installation to
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a new version. Before version 9.1 dump and restore was needed which
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was much slower.
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pg_upgrade needs to have the server binaries of both versions
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available. To allow this, we had to change the way PostgreSQL is
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packaged as well as the naming of the packages, so that two or more
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versions of PostgreSQL can be installed in parallel. The package
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names for PostgreSQL contain numbers indicating the major version.
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In PostgreSQL terms for versions up to 9.6 the major version consisted
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of the first two components of the three-component version number,
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i.e. 8.3, 8.4, 9.0, or 9.1. So, the packages for Postgresql 9.1 are
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named postgresql91, postgresql91-server, etc. Inside the packages the
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files were moved from their standard locations to a versioned location
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such as /usr/lib/postgresql83/bin or /usr/lib/postgresql91/bin to
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avoid file conflicts if packages are installed in parallel.
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Starting with version 10 the PostgreSQL project changed their
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versioning scheme from from three components to two, which means one
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component for the major version and one for the minor. So, the
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sequence of major version across the versioning scheme change will be:
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9.4, 9.5, 9.6, 10, 11, 12. For versions that use the new versioning
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scheme SUSE only puts the single component major version into the
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package name, so the postgresql96 package (containg version 9.6
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according to the old versioning scheme) will be followed by
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postgresql10, then postgresql11, and so on.
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The update-alternatives mechanism creates and maintains symbolic links
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that cause one version (by default the highest installed version) to
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re-appear in the standard locations. By default, database data are
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stored under /var/lib/pgsql/data on SUSE Linux.
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The following preconditions have to be fulfilled before data migration
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can be started:
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1. If not already done, the packages of the old PostgreSQL version
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must be upgraded to the new packaging scheme through a maintenance
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update.
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2. The packages of the new PostgreSQL major version need to be
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installed. As pg_upgrade is contained in postgresql91-contrib, that
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one has to be installed as well, at least until the migration is
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done.
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3. Unless pg_upgrade is used in link mode, the server must have
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enough free disk space to temporarily hold a copy of the database
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files. If the database instance was installed in the default
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location, the needed space in megabytes can be determined by running
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the follwing command as root: "du -hs /var/lib/pgsql/data". If space
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is tight, it might help to run the "VACUUM FULL" SQL command on each
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database in the instance to be migrated, but be aware that it might
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take very long.
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The latest upstream documentation for pg_upgrade including step by
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step instructions for performing a database migration can be found
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online under https://www.postgresql.org/docs/current/pgupgrade.html ,
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or locally under
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file:///usr/share/doc/packages/postgresqlXX/html/pgupgrade.html , if
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the postgresqlXX-docs package is installed. XX is a place holder for
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the respective major version here.
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NOTE: The online documentation starts with explaining how you can
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install PostgreSQL from the upstream sources (which is not necessary
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when you install the SUSE RPMs) and also uses other directory names
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(/usr/local instead of the update-alternatives based path as described
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above).
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For background information about the inner workings of pg_upgrade and
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a performance comparison with the old dump and restore method, see
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http://momjian.us/main/writings/pgsql/pg_upgrade.pdf .
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