postgres_psycopg2 adapter should not use hard coded isolation levels

[limscoder]

Django's postgres_psycopg2 adapter sets the connection's isolation level to psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED when autocommit == False.

My application requires a more strict isolation level, so I am forced to create a new backend and override DatabaseWrapper._set_isolation_level to make sure the connection has the correct isolation level set.

There should be a configuration option within the database config in settings.py that allows users to set the appropriate isolation level if the default level is not correct for their application. It would also be nice if there was an option to not set the isolation level at all, and instead rely on the default isolation level provided by the Postgres server.

[Andrei Antoukh]

Here the patch to allow to define the default isolation_level parameter on database configuracion dict: ​https://github.com/niwibe/django/compare/issue_18130

I run the tests (not all tests) and I have not seen any fail that might be related.

[Aymeric Augustin]

Yes, we could provide a way to switch to "serializable" for people with high concurrency and integrity requirements.

IIRC, under the "serializable" isolation level, the application should be prepared to handle transaction failures (and possibly retry) on every database query. I'm not sure we can handle this automatically in Django without introducing magic. It deserves a fat warning in the documentation. This isolation level is for people who know what they're doing :)

NB: there is some material on this topic in #3460.

[Andrei Antoukh]

I think, does not need any kind of magic by django, as you say: "This isolation level is for people who know what they're doing."

I now update the patch with some checks for isolation_level value and documentation notes with warning.

[Aymeric Augustin <aymeric.augustin@…>]

In e0449316ebacaa550e9c529f8c9cb9a9b44e3765:

Fixed #18130 -- Made the isolation level configurable on PostgreSQL.

Thanks limscoder for the report and niwi for the draft patch.