Make sure migration is atomic #25

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opened 2020-01-26 20:12:56 +01:00 by midgard · 6 comments

midgard commented

2020-01-26 20:12:56 +01:00

(Migrated from git.zeus.gent)

https://docs.sqlalchemy.org/en/13/orm/session_api.html#sqlalchemy.orm.session.sessionmaker

https://docs.sqlalchemy.org/en/13/orm/session_transaction.html#unitofwork-transaction

But migrations use methods of module alembic and not SQL Alchemy directly.

https://docs.sqlalchemy.org/en/13/orm/session_api.html#sqlalchemy.orm.session.sessionmaker https://docs.sqlalchemy.org/en/13/orm/session_transaction.html#unitofwork-transaction But migrations use methods of module `alembic` and not SQL Alchemy directly.

midgard commented

2020-01-26 20:12:56 +01:00

(Migrated from git.zeus.gent)

changed milestone to %1

midgard commented

2020-01-26 20:24:12 +01:00

(Migrated from git.zeus.gent)

changed the description

midgard commented

2020-01-26 22:29:19 +01:00

(Migrated from git.zeus.gent)

This depends on the DDL. MySQL is non-transactional by Alembic's design. Nowadays MySQL does support transactions so Alembic should probably be changed.

midgard commented

2020-01-26 22:29:54 +01:00

(Migrated from git.zeus.gent)

As a workaround we could emit START TRANSACTION; and COMMIT; manually at the start and end of the migration.

As a workaround we could emit `START TRANSACTION;` and `COMMIT;` manually at the start and end of the migration.

midgard commented

2020-01-26 22:40:16 +01:00

(Migrated from git.zeus.gent)

Turns out, transactions in MySQL suck. E.g. CREATE TABLE can't be rolled back.

Thus, we cannot ensure atomic migrations.

Turns out, transactions in MySQL suck. E.g. `CREATE TABLE` can't be rolled back. Thus, we cannot ensure atomic migrations.

midgard commented