allow_unsafe_locale: true still enforces the check on postgres' encoding

[erkinalp]

Description

allow_unsafe_locale still fails to work when a non-C locale is supplied.

Steps to reproduce

• Run Synapse with YugabyteDB as the database
• Observe it fails to work because Yugabyte storage actually does not support C collation

Homeserver

local test setup

Synapse Version

1.66.0

Installation Method

Docker (matrixdotorg/synapse)

Platform

Yugabyte is also from the latest docker.

Relevant log output

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/synapse/app/homeserver.py", line 382, in setup
    hs.setup()
  File "/usr/local/lib/python3.9/site-packages/synapse/server.py", line 308, in setup
    self.datastores = Databases(self.DATASTORE_CLASS, self)
  File "/usr/local/lib/python3.9/site-packages/synapse/storage/databases/__init__.py", line 74, in __init__
    prepare_database(
  File "/usr/local/lib/python3.9/site-packages/synapse/storage/prepare_database.py", line 152, in prepare_database
    _setup_new_database(cur, database_engine, databases=databases)
  File "/usr/local/lib/python3.9/site-packages/synapse/storage/prepare_database.py", line 213, in _setup_new_database
    database_engine.check_new_database(cur)
  File "/usr/local/lib/python3.9/site-packages/synapse/storage/engines/postgres.py", line 137, in check_new_database
    raise IncorrectDatabaseSetup(
synapse.storage.engines._base.IncorrectDatabaseSetup: Database is incorrectly configured:

    - 'CTYPE' is set to 'en_US.UTF-8'. Should be 'C'

See docs/postgres.md for more information.
******************************************************
 Error during initialisation:
    Database is incorrectly configured:
 
     - 'CTYPE' is set to 'en_US.UTF-8'. Should be 'C'
 
 See docs/postgres.md for more information.
 There may be more information in the logs.
******************************************************

Anything else that would be useful to know?

No response

[erkinalp]

Corresponding yugabyte issue: yugabyte/yugabyte-db#13863

[erkinalp]

[DMRobertson]

See #12055 for motivation. I think most people would expect there to be a single i_know_what_im_doing_and_accept_possible_data_corruption flag, and so we'd probably accept a PR which

• made this flag also disable the check on SERVER_ENCODING
• updated docs accordingly.

Note that we have no plans to support databases other than Postgres and Sqlite, not even those which aim to be wire-compatible with Postgres.