Previously, a failed backup would always overwrite ${db}.sql.gz,
because the bash `>` redirect truncates the file; even if the
backup was going to fail.
On the next run, the ${db}.prev.sql.gz backup would be
overwritten by the bad ${db}.sql.gz.
Now, if the backup fails, the ${db}.in-progress.sql.gz is in an
unknown state, but ${db}.sql.gz will not be written.
On the next run, ${db}.prev.sql.gz (our only good backup) will
not be overwritten because ${db}.sql.gz does not exist.
Or … none! Because forcing a string always results in an OnCalender=
setting, but an empty string leads to an empty value.
> postgresqlBackup-hass.timer: Timer unit lacks value setting. Refusing.
or
> postgresqlBackup-miniflux.timer: Cannot add dependency job, ignoring: Unit postgresqlBackup-miniflux.timer has a bad unit file setting.
I require the postgresqlBackup in my borgbackup unit, so I don't
strictly need the timer and could previously set it to an empty list.
A centralized list for these renames is not good because:
- It breaks disabledModules for modules that have a rename defined
- Adding/removing renames for a module means having to find them in the
central file
- Merge conflicts due to multiple people editing the central file
For large setups it is useful to list all databases explicit
(for example if temporary databases are also present) and store them in extra
files.
For smaller setups it is more convenient to just backup all databases at once,
because it is easy to forget to update configuration when adding/renaming
databases. pg_dumpall also has the advantage that it backups users/passwords.
As a result the module becomes easier to use because it is sufficient
in the default case to just set one option (services.postgresqlBackup.enable).
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
