[DPE-5301] Add check for low storage space on pgdata volume

[lucasgameiroborges]

Issue

The charm gives no indication of low storage space on pgdata folder, which can cause unexpected failures

Solution

Added check on update_status hook + integration test.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 6 lines in your changes missing coverage. Please review.

Project coverage is 70.65%. Comparing base (5db6b05) to head (0699c45).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/charm.py	66.66%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #685      +/-   ##
==========================================
- Coverage   70.72%   70.65%   -0.07%     
==========================================
  Files          11       11              
  Lines        2951     2968      +17     
  Branches      514      517       +3     
==========================================
+ Hits         2087     2097      +10     
- Misses        754      760       +6     
- Partials      110      111       +1     

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[dragomirp]

We should most probably don't change the status in _set_active_status() if the message is INSUFFICIENT_SIZE_WARNING and then reset the status here before running _set_active_status().

This is because if another hook runs _set_active_status() the status will be overwritten unite the next update status. @marceloneppel what do you think?

[lucasgameiroborges]

I'm not sure I understand your point. Could you elaborate? My motivation for this check is to resolve the blocked status in case the storage space got released (to >10%)

[lucasgameiroborges]

the check for INSUFFICIENT_SIZE_WARNING is just to make sure that, if the charm was blocked due to insufficient size but the user has released enough space, then resolve. Maybe there's a better way?

[marceloneppel]

I think it's a good idea, @dragomirp.

@lucasgameiroborges, the idea is to just set something else in the status at this point, like the Active Status, and put a condition in the _set_active_status method not to change the status to Active if the current status is INSUFFICIENT_SIZE_WARNING. This way, we avoid some other places overring this status incorrectly (maybe here).

I see that this will need to be handled correctly later by improving how we manage the unit's statuses across the entire charm code.

[lucasgameiroborges]

I get the reasoning for including a check inside _set_active_status so the blocked status doesn't get overwritten in other places, as for just set something else in the status at this point, like the Active Status do you mean using self.unit.status = ActiveStatus() directly? why?

[dragomirp]

The elif should be something like:

        elif self.unit.status.message == INSUFFICIENT_SIZE_WARNING:
            self.unit.status = ActiveStatus()
            self._set_active_status()

if _set_active_status() preserves INSUFFICIENT_SIZE_WARNING it should be unset before calling it. Otherwise it won't unset.

[taurus-forever]

Q: are we moving the right way here?
It smells like Status/Message manipulation is going outside of our control.

[lucasgameiroborges]

Oh! Now I see the problem! Yes of course, thanks @dragomirp and @marceloneppel !

@taurus-forever : I agree that status management is a bit all over the place. AFAIK this is a problem in other charms too. Interesting discussion here: https://chat.canonical.com/canonical/pl/ncbsrryk378jux5r8cxjjngzna