On Thu, Feb 10, 2011 at 3:46 PM, David E. Wheeler <da...@kineticode.com> wrote: > On Feb 10, 2011, at 12:07 PM, Robert Haas wrote: > >> You don't need them to be sortable. You just need them to be >> comparable, and equality seems like a plenty good enough comparison >> rule. You can compute the shortest chain of upgrade scripts that can >> take you from the current version to the target version. > > You have to be able to apply them in order. Unless I'm missing something, > that means you need to be able to sort them.
Not at all. Say the currently installed version of the "dungeon" extension is "kobold" and you want to upgrade to "bugbear". You have the following scripts: dungeon-goblin-orc.sql dungeon-hobgoblin-bugbear.sql dungeon-kobold-goblin.sql dungeon-orc-hobgoblin.sql Now, it's pretty clear that the only way to get to bugbear is to come from hobgoblin, and the only way to get to hobgoblin is to come from orc. orc can be reached only from goblin, which can be reached only from kobold. So it's 100% clear that you have to apply the scripts in the following order: dungeon-kobold-goblin.sql dungeon-goblin-orc.sql dungeon-orc-hobgoblin.sql dungeon-hobgoblin-bugbear.sql Note that this even works if the versions aren't totally ordered. For example, suppose you release version 0.1 of a module and later you release a 1.0, which unfortunately is incompatible: there's no upgrade path from 0.1 to 1.0. In time, 1.0 is superseded by 1.1. And then you make some improvements to the old 0.1 code base and release that as 0.2. Finally, you come up with an idea for unifying the two and release a 1.2 version, which supports upgrades from all the previous versions. You just ship: foo-0.1-0.2.sql foo-0.2-1.2.sql foo-1.0-1.1.sql foo-1.1-1.2.sql If the user asks to upgrade to version 1.2, we'll observe that you can get to 1.2 from 1.1 or from 0.2. Not knowing what the version numbers mean, we'll look a bit further and see that you can get from 1.0 to 1.1 or from 0.1 to 0.2. Thus you can get to 1.2 like this: 0.1 -> 0.2 -> 1.2 0.2 -> 1.2 1.0 -> 1.1 -> 1.2 1.1 -> 1.2 -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
