A major-level upgrade is slightly different from a minor version upgrade. As a quick reminder, definitely go and read the upgrade notes; major versions will always have some. Remember about the What's new pages, too.
Back to the major version upgrade itself, the most significant differences from a minor version upgrade are as follows:
- Database schema changes
- Compatibility
- Reading the upgrade notes
Let's talk about database schema changes right now, let's discuss compatibility in detail a bit later, and let's always remember to read our upgrade notes.
While the Zabbix team works hard to keep minor version upgrades without database changes, for major releases, it's open season. Changes to the database schema and its contents are made to accommodate new features, improve performance, and increase flexibility. Users wouldn't appreciate it if they couldn't keep gathered data and created configuration in the name of new greatness so, with each new version, a database upgrade patch is provided. This may include adding new tables and columns, removing tables and columns, and changing the data layout.
Given that a major version upgrade changes the database, make sure you have a recent backup. While upgrades are extensively tested, it isn't possible for the developers to test all scenarios. What has worked for a thousand people might break in some obscure way for you. Additionally, interrupting the upgrade process because of a hardware or electricity failure is likely to leave your database in a broken state. You've been warned, so get that backup ready.
You're strongly encouraged to test the upgrade on a test installation, preferably using a production dataset (maybe with trimmed history and trend data, if the available hardware doesn't permit testing with a full copy).
With a fresh backup created, we're ready to engage the major version upgrade. The database upgrade process significantly changed for Zabbix version 2.2. In older versions, we had to apply the database patch manually. If you happen to have an old Zabbix installation—old being pre-2.0—you'll have to patch it up to the 2.0 database schema manually. For your reference, the database patches are located in the upgrades/dbpatches directory in the source tree, but if you really want to follow that path, make sure to consult with the Zabbix community via the channels discussed in Appendix B, Being Part of the Community.
For upgrading to Zabbix from version 2.2 or more recent, no manual patching is required. Starting up the new server will automatically upgrade the database schema. Note that this database upgrading happens without a confirmation. Be careful not to start a more recent server binary against an older database version if you don't intend to change the database.
One last note regarding the upgrade notes: promise. While the latest Zabbix upgrades are really quick even in large installations, older versions sometimes upgraded historical data tables, and that took a long time—like, really a long time. In some reported cases, it was days. If such a change is required in any of the future versions, it'll be mentioned in the upgrade notes, and you'll be glad you read them.