#30490: migrations unique_index on (app, name).
-------------------------------------+-------------------------------------
Reporter: Richard | Owner: nobody
Kojedzinszky |
Type: Bug | Status: new
Component: Uncategorized | Version: master
Severity: Normal | Resolution:
Keywords: migrations parallel | Triage Stage:
run | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by Richard Kojedzinszky):
* status: closed => new
* resolution: wontfix =>
Comment:
Unfortunately, knowing that the migration tasks and recording its
existence is not run in the same transaction, in a worst case scenario,
the info that a migration has been applied can be lost at all. So, in any
circumstances, they should be in the same transaction.
Replying to [ticket:30490 Richard Kojedzinszky]:
> I've a django based api service. I run it in containers, in kubernetes.
When I update my image, basically I run the migiration process, then start
the application. With k8s for example, when I start the deployment with 2
or more replicas, actually 2 parallel running migration process will
start. With the following very simple migration process, unfortunately the
migration will be applied twice:
>
> {{{
> from django.db import migrations
> from django.db.models import F
> import time
>
> def forward(apps, schema_editor):
> TT = apps.get_model('center', 'TestTable')
> time.sleep(10)
> TT.objects.all().update(value=F('value') + 1)
>
> def backward(apps, schema_editor):
> TT = apps.get_model('center', 'TestTable')
> TT.objects.all().update(value=F('value') - 1)
>
>
> class Migration(migrations.Migration):
>
> dependencies = [
> ('center', '0007_testtable'),
> ]
>
> operations = [
> migrations.RunPython(forward, backward)
> ]
> }}}
>
> Even if the migration process is ran in a transaction, due to the unique
index missing, it will be applied multiple times.
>
> Even though my setup may be rare, I think it would really be necessary
to prevent migrations to be applied more than once. Db unique_together
could be utilized for that.
--
Ticket URL: <https://code.djangoproject.com/ticket/30490#comment:3>
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