Hi, so I added a quick recipe to the site just now just so that the "set search path" idea is documented to some extent, that is at https://alembic.sqlalchemy.org/en/latest/cookbook.html#rudimental-schema-level-multi-tenancy-for-postgresql-databases .
Re: autogenerate, if you have many schemas that all contain an exact copy of the same schema, then autogenerate implies you'd be running this exactly once for just one of the schemas, or a "master" schema, such that you generate the .py files that will then be applicable to all the schemas. The recipe above discusses this, and in particular it works in a completely schema agnostic fashion, you would set include_schemas=False in the config and allow the PostgreSQL search_path to handle all movement between schemas. then for the actual migration "upgrade" run, you would run those files against each schema in sequence, again making use of search_path in order to select each schema. as far as how alembic is looking at current tables you would need to turn on SQL logging, using the "debug" level, such as in alembic.ini (if you're using that): [logger_sqlalchemy] level = DEBUG handlers = qualname = sqlalchemy.engine this will emit a lot of queries and result sets. You'd have to capture that logging and then grep through for the "nonexistent" schema - it will be present in a result set that Alembic is capturing, most fundamentally the one it uses to get all the schema names. On Tue, Sep 29, 2020, at 4:01 PM, Daniel Krebs wrote: > Hi Mike, > > thanks a bunch for the quick response! > > >> This is supported by SQLAlchemy more robustly using the > >> schema_translate_map feature, see > >> https://docs.sqlalchemy.org/en/13/core/connections.html#schema-translating > >> . this feature allows schema names to render explicitly without the > >> need to manipulate search_path. > > > > this feature may not work completely with Alembic however, I'm > > evaluating that now. > > > > still doesnt shed any light on your sporadic problem, however. > > It's been some time already since I've implemented this, so can't recall > the exact reason why I went down that road but I know for sure that I > was trying to make it work with schema_translate_map but didn't succeed. > I would have very much preferred a solution without patching alembic it > seemed to my last resort at the time. I'd be more than happy to find a > solution here :) > > > > However, when using that approach you'd normally be running > autogenerate from just one schema, since you are looking to generate > migrations just once and then run them on every tenant. > > > > so it's not clear why autogenerate is being run on every tenant > explicitly - you'd have just one "model" schema that's the one where you > actually run autogenerate upon. there would be no need to consider > other schemas and include_schemas would be set to False. > > Indeed that sounds like a good idea. So you'd suggest to keep one schema > just for autogeneration purposes and then apply the migrations to all > customer schemas? Is that possible from within alembic or would you wrap > some tooling around alembic in order to apply migrations one-by-one to > every schema? > > > > As far as being able to filter out schemas across many, the current > approach is the include_object hook, which is insufficient for many > schemas as it does not block the reflection of all the tables. a new > hook include_name is being added in the coming weeks that allows for > pre-emptive inclusion or exclusion of specific schema names. > > I tried the include_object hook back then, but I was facing reflection > issues if I remember correctly. We're using TimescaleDB [1] in the same > database which adds some schemas of its own that alembic doesn't seem to > be able to handle. > > > > I don't have much insight onto this other than looking at concurrent > activities on the database. "sometimes" usually indicates a race > condition of some sort, and the "autogenerate" process is strictly one > of reading data. > > Indeed I'm suspecting the same thing. However, I'm not the most > knowledgable DBA nor do I have an understanding of how alembic actually > compares the current state of the DB with the SA models. Could you maybe > provide a more concrete point what and where to look for? > > > Thank you for taking the time to help! > > > Cheers, > Daniel > > [1] https://www.timescale.com/ > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy-alembic" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sqlalchemy-alembic+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sqlalchemy-alembic/fc2bc5e4-274b-a9e7-0566-3b745c4e5fc5%40enlyze.com. > -- You received this message because you are subscribed to the Google Groups "sqlalchemy-alembic" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy-alembic+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sqlalchemy-alembic/cc68de85-ebf3-4eb7-bf83-35b8082a80e4%40www.fastmail.com.
