However, you don't really need me to tell you that, because it's in the language of the release. More on this below.
A couple of notable fixes in this release:
Hstore-JSON extension fix: if you are using both Hstore and JSON in Postgres 9.3, you should run ALTER EXTENSION hstore UPDATE after updating your server. Due to a mistake in extension versioning, users missed out on some JSON-hstore conversion functions in 9.3.
Guarantee transmission of all WAL files: users with replication setups and stringent data retention requirements will want to apply the update sooner rather than later because of this fix. It fixes an issue where under some circumstances a promoted replica might ignore a few transactions it actually received from the master before failover, considering them lost.
Over the last dozen or so update releases, we've standardized the language we use to explain how critical the fixes in the release are for most users.
First, there's the question of what kind of update it is:
Bugfix Release or Update Release: this usually contains two to four months of accumulated bug fixes for various reported bugs. Some of these bugs may be critical data loss bugs; see the release contents to check this.
Security Release: the update contains a patch for one or more security holes. This makes the update at least somewhat urgent, because as soon as the security patch is posted online, the black hats start working on exploits (assuming they didn't before then).
Then we use some standard language about the general criticality of bugs fixed in the release:
All users of the affected versions are strongly urged to apply the update immediately: release contains a high-exposure security hole or critical data loss bug which affects all users. Stop reading, declare a downtime, and apply the update now. Fortunately, we've only had one of these in the last 6 years.
All users should apply this update as soon as possible: the release contains one or more security holes and/or major data loss bugs expected to affect most users. Schedule a downtime tonight or this weekend and apply the update.
All users of _________ should apply this update immediately/as soon as possible: the same as above, but only for users of a particular feature or extension.
Users should apply this update at the next available opportunity: the release contains some low-risk security holes and/or serious data loss bugs which only occur under certain circumstances. Updating to this release shouldn't be put off for more than a couple weeks, but you can wait for a good low-traffic window to take the downtime.
Users should update at the next regular maintenance window/scheduled downtime: this update contains nothing critical or even serious for most users; it's largely a cumulative collection of bugfixes. The update should be added to the general queue of OS, library and application updates for the production servers.
Note, however, that I said most users. Every update we push out is urgent for at least a few users who are hit by the specific bugs involved. For example, for the current release, users who depend heavily on the following features should consider updating sooner rather than later:
- Range indexes
- regular expressions
- prepared query plans
- SSL connections
- more than 24GB (!) of work memory
That's why we're reluctant to adopt any system which rates update releases on some absolute scale. It doesn't matter how critical the update is in general; it matters how critical it is to you.