Optionally move the old cluster

If you are using a version-specific installation directory, e.g. /opt/PostgreSQL/8.4, you do not need to move the old cluster. The one-click installers all use version-specific installation directories.

If your installation directory is not version-specific, e.g. /usr/local/pgsql, it is necessary to move the current PostgreSQL install directory so it does not interfere with the new PostgreSQL installation. Once the current PostgreSQL server is shut down, it is safe to rename the PostgreSQL installation directory; assuming the old directory is /usr/local/pgsql, you can do:

mv /usr/local/pgsql /usr/local/pgsql.old

to rename the directory.

For source installs, build the new version

Build the new PostgreSQL source with configure flags that are compatible with the old cluster. pg_upgrade will check pg_controldata to make sure all settings are compatible before starting the upgrade.

Install the new PostgreSQL binaries

Install the new server's binaries and support files. You can use the same port numbers for both clusters, typically 5432, because the old and new clusters will not be running at the same time.

For source installs, if you wish to install the new server in a custom location, use the prefix variable:

gmake prefix=/usr/local/pgsql.new install

Install pg_upgrade and pg_upgrade_support

Install pg_upgrade and pg_upgrade_support in the new PostgreSQL cluster

Initialize the new PostgreSQL cluster

Initialize the new cluster using initdb. Again, use compatible initdb flags that match the old cluster. Many prebuilt installers do this step automatically. There is no need to start the new cluster.

Install custom shared object files

Install any custom shared object files (or DLLs) used by the old cluster into the new cluster, e.g. pgcrypto.so, whether they are from contrib or some other source. Do not install the schema definitions, e.g. pgcrypto.sql, because these will be migrated from the old cluster.

Adjust authentication

pg_upgrade will connect to the old and new servers several times, so you might want to set authentication to trust in pg_hba.conf, or if using md5 authentication, use a ~/.pgpass file (see Section 31.14) to avoid being prompted repeatedly for a password.

Stop both servers

Make sure both database servers are stopped using, on Unix, e.g.:

pg_ctl -D /opt/PostgreSQL/8.4 stop
pg_ctl -D /opt/PostgreSQL/9.0 stop

or on Windows, using the proper service names:

NET STOP postgresql-8.4
NET STOP postgresql-9.0

or

NET STOP pgsql-8.3  (PostgreSQL 8.3 and older used a different service name)

Run pg_upgrade

Always run the pg_upgrade binary of the new server, not the old one. pg_upgrade requires the specification of the old and new cluster's data and executable (bin) directories. You can also specify separate user and port values, and whether you want the data linked instead of copied (the default). If you use linking, the migration will be much faster (no data copying), but you will no longer be able to access your old cluster once you start the new cluster after the upgrade. See pg_upgrade --help for a full list of options.

For Windows users, you must be logged into an administrative account, and then start a shell as the postgres user and set the proper path:

RUNAS /USER:postgres "CMD.EXE"
SET PATH=%PATH%;C:\Program Files\PostgreSQL\9.0\bin;

and then run pg_upgrade with quoted directories, e.g.:

pg_upgrade.exe
        --old-datadir "C:/Program Files/PostgreSQL/8.4/data"
        --new-datadir "C:/Program Files/PostgreSQL/9.0/data"
        --old-bindir "C:/Program Files/PostgreSQL/8.4/bin"
        --new-bindir "C:/Program Files/PostgreSQL/9.0/bin"

Once started, pg_upgrade will verify the two clusters are compatible and then do the migration. You can use pg_upgrade --check to perform only the checks, even if the old server is still running. pg_upgrade --check will also outline any manual adjustments you will need to make after the migration. pg_upgrade requires write permission in the current directory.

Obviously, no one should be accessing the clusters during the migration.

If an error occurs while restoring the database schema, pg_upgrade will exit and you will have to revert to the old cluster as outlined in step 14 below. To try pg_upgrade again, you will need to modify the old cluster so the pg_upgrade schema restore succeeds. If the problem is a contrib module, you might need to uninstall the contrib module from the old cluster and install it in the new cluster after the migration, assuming the module is not being used to store user data.

Restore pg_hba.conf

If you modified pg_hba.conf to use trust, restore its original authentication settings.

Post-migration processing

If any post-migration processing is required, pg_upgrade will issue warnings as it completes. It will also generate script files that must be run by the administrator. The script files will connect to each database that needs post-migration processing. Each script should be run using:

psql --username postgres --file script.sql postgres

The scripts can be run in any order and can be deleted once they have been run.

Statistics

Because optimizer statistics are not transferred by pg_upgrade, you will be instructed to run a command to regenerate that information at the end of the migration.

Delete old cluster

Once you are satisfied with the upgrade, you can delete the old cluster's data directories by running the script mentioned when pg_upgrade completes. You can also delete the old installation directories (e.g. bin, share).

Reverting to old cluster

If, after running pg_upgrade, you wish to revert to the old cluster, there are several options:

• If you ran pg_upgrade with --check, no modifications were made to the old cluster and you can re-use it anytime.

• If you ran pg_upgrade with --link, the data files are shared between the old and new cluster. If you started the new cluster, the new server has written to those shared files and it is unsafe to use the old cluster.

• If you ran pg_upgrade without --link or did not start the new server, the old cluster was not modified except that an .old suffix was appended to $PGDATA/global/pg_control and perhaps tablespace directories. To reuse the old cluster, remove the .old suffix from $PGDATA/global/pg_control. and, if migrating to 8.4 or earlier, remove the tablespace directories created by the migration and remove the .old suffix from the tablespace directory names; then you can restart the old cluster.