[bug#45860] Improve PostgreSQL service.

[Christopher Baines <mail@cbaines.net>]

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Mathieu Othacehe <othacehe@gnu.org> writes:

> Hello Chris,
>
>> I haven't read through these changes in detail, but the mixing of the
>> record describing the config file, and the record for configuring the
>> service introduces the limitation that you can no longer specify any
>> lowerable object (like a file) or something like a string to use a
>> config file outside of the store. Did you have a reason for mixing the
>> records together?
>
> I must admit I overlooked that possibility. The reason for merging the
> records is that the "log-destination" is now needed both to enable
> "pg_ctl" logging in "postgresql-shepherd-service" and in
> "postgresql-config-file" to be written in PostgreSQL configuration.
>
> Plus having a record called <postgresql-configuration> that does not
> contain some of the configuration field feels weird.
>
> Is passing a lowerable config file a use case of yours? In that case I
> could still add a "raw-config" field to override the configuration file
> creation.

It's not, however given I'm able to make changes to the service
definition, that's what I generally do when I have a problem with it,
rather than sidestepping the Guix configuration layer. It's hard to tell
if anyone is doing that or not.

This pattern of using a record with a gexp-compiler is used for quite a
few services now, but mostly because I've implemented quite a few
services (I think there's one case where someone else did similarly).

I get that there's some value in trying to help users by creating the
relevant directory for logs, but I'm not sure it requires all these
changes.

I'm also unsure about using the same names for configuration parameters,
but picking different semantics. log-destination [1] can be a list
(comma separated string), which I reasonably could be "stderr,syslog" or
'(stderr syslog) in the Guix configuration (just as an example), and
with the service changes proposed here the string value would mean that
log_directory gets set to "stderr,syslog" which seems wrong.

1: https://www.postgresql.org/docs/13/runtime-config-logging.html#GUC-LOG-DESTINATION

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