Replication & Upgrades - PostgreSQL 9 Administration - page 327

2. If you have professional support, speak to your support vendor to see if
additional safety checks over and above the upgrade instructions are required or
recommended, if any. Check also that the target release is fully supported by your
vendor on your hardware and OS and OS release level; it may not be, yet.
3. Apply any special actions or checks, for example if WAL format has changed, then
you may need to reconfigure log based replication following the upgrade. You may
need to scan tables, rebuild indexes or some other action. Not every release has such
actions, but watch closely for them, because if they exist, then they are important.
4. If you are using replication, test the upgrade by shutting down one of your Standby or
slave servers.
5. Follow the instructions for your OS distribution and binary packager to complete the
upgrade. These can vary considerably.
6. Startup the database server being used for a test, apply any post-upgrade special
actions, and check that things are working for you.
7. Follow steps 4 to 6 for other Standby servers.
8. Follow steps 4 to 6 for the Primary server.
How it works...
Minor upgrades mostly affect the binary files, so it should be a simple matter of replacing
those files and restarting. But check.
Major upgrades in-place
New in PostgreSQL 9.0 is a utility named pg_upgrade , supplied as a contrib module. pg_
upgrade allows you to migrate to new major versions of PostgreSQL, such as from 8.4 to 9.0,
or from 9.0 to 9.1.
In-place upgrades means upgrading your database without moving to a new system. That
does sounds good, though pg_upgrade has a few things that you may wish to consider as
potential negatives, which are as follows:
F Database server must be shut down while upgrade takes place.
F Your system must be big enough to hold two copies of the database server: old and
new copies. If it's not, then you have to use the link option of pg_upgrade , or
use the recipe on upgrading using replication tools. If you use the link option on
pg_upgrade , then there is no pg_downgrade utility. The only option is a restore
from backup, and that means extended unavailability if that occurs.
F If you copy the database, then upgrade, time will be proportional to the size
of the database.
F pg_upgrade only supports PostgreSQL 8.3+.