You may have noticed that we've had a lot of churn in PostgreSQL update releases lately, doing three updates in less than two months. We expect that we're done with that now, so it's time to get on updating all of your servers with today's update release.
Users of PostgreSQL 9.3 and 9.4 should update this weekend if possible. This cumulative update fixes several problems with our "multixact" mechanism which have been plaguing Postgres since the release of 9.3.0. While most users will not hit these issues, if you do, the bugs cause unrecoverable data corruption. In other words, waiting "until you see a problem" is a really, really bad idea.
Additionally, one of the problems fixed requires cleaning up some garbage left by the version of pg_upgrade which shipped with Postgres versions 9.3.0 to 9.3.4. If you used pg_upgrade to upgrade to one of those versions -- even if you subsequently upgraded to 9.4 -- then the server is liable to trigger a database-wide all-table autovacuum as soon as you restart after applying 9.3.9 or 9.4.2.
If you are prepared for minutes to hours of degraded performance after applying the update, this is not a problem. If it is a problem, though, you can do precautionary vacuuming before you apply the update. Detailed instructions are supplied in the release notes on how to do this.
Now, go update those servers!