Document how to setup a local Postgres DB

[glatterf42]

Working on the ixmp shim, I realized that we will need a guide on how to setup a local postgres DB. It seems we store theses guides in the advanced install instructions here, so I'm opening this PR to accompany iiasa/ixmp#601.

How to review

• Read the diff and note that the CI checks all pass.
• Check the Postgres section in the advanced install instructions in the RTD build for errors and clarity.

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation.
• Update release notes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.5%. Comparing base (f97e386) to head (dbcb8af).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #981     +/-   ##
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- Coverage   96.5%   96.5%   -0.1%     
=======================================
  Files         60      60             
  Lines       5155    5155             
=======================================
- Hits        4976    4975      -1     
- Misses       179     180      +1     

see 1 file with indirect coverage changes

[khaeru]

Can we use SemBr?

[glatterf42]

Done, I hope :)

[khaeru]

What I would wonder is: at what point, and how, should one enter these values into the ixmp configuration, such that ixmp4 will connect to this database?

[glatterf42]

Not sure, to be honest. In the test suite, platforms are added to ixmp4 using a --dsn that includes these values, but then the migrations are run using IXMP4_MANAGED=False because locally on my system, running them without this produces an error.
The ixmp platforms are then created dynamically as the tests need them, hardcoding the values.

For "real world users", I think the values should be provided much like they are now: one needs to enter a platform name and credentials to the ixmp config (e.g. using the CLI or by manually editing the config file) before one can connect to the underlying DB.
It seems to me that we mainly need a test to ensure that ixmp reads these values correctly and passes them on to ixmp4.

What keeps me from doing that is my lack of understanding/familiarity with the authentication system in ixmp4. I'm not quite sure how it works and if it works at all when not using the RestAPI layer (but the DB layer directly, either directly directly or via the core layer). Maybe @meksor knows what's missing to test this/get it to work.

[khaeru]

Thanks for this addition!

I made some edits to clarify a few points, including:

• The section is only relevant when using IXMP4Backend.
• The relationship between the DSN configuration and the arguments to the docker run command.
• Data persistence across container restarts.