#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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Comment (by Richard Kojedzinszky):
Perhaps, a similar patch would be a good starting point:
https://github.com/rkojedzinszky/django/commit/12477598fb3711f50ff482328ddcda62934caee6
Replying to [comment:3 Richard Kojedzinszky]:
>
> 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:4>
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