id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
30490	migrations unique_index on (app, name).	Richard Kojedzinszky	nobody	"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."	Bug	closed	Uncategorized	dev	Normal	wontfix	migrations parallel run	Adam Johnson	Unreviewed	0	0	0	0	0	0