We have updated the restart policy for managed PostgreSQL servers: deferred restarts remain the norm, but we restart immediately in case of updates to the PostgreSQL package itself.
The reason behind this decision is a unfortunate experience we’ve made during the last PostgreSQL security update. In the course of the security update a new PostgreSQL version has been installed, but the old version kept running until the scheduled restart was due. During this time, customers experienced strange errors: some server functions tend to open files dynamically, but file contents differed from the server’s expectations. This led to unexpected behaviour that was hard to debug.
Please note that this affects only (security) updates to PostgreSQL itself which are very infrequent. All other reasons to restart PostgreSQL, like updated libraries (for which an old version is kept) or configuration changes, cause scheduled maintenance as always.