Update multiple objects at once in Django?

Atomic transactions can reduce the time spent in the loop:

from django.db import transaction

with transaction.atomic():
    for i, row in df.iterrows():
        mv = MeasureValue.objects.get(org=row.org, month=month)

        if (row.percentile is None) or np.isnan(row.percentile): 
            # if it's already None, why set it to None?
            row.percentile = None

        mv.percentile = row.percentile
        mv.save()

Django’s default behavior is to run in autocommit mode. Each query is immediately committed to the database, unless a transaction is actives.

By using with transaction.atomic() all the inserts are grouped into a single transaction. The time needed to commit the transaction is amortized over all the enclosed insert statements and so the time per insert statement is greatly reduced.

As of Django 2.2, you can use the bulk_update() queryset method to efficiently update the given fields on the provided model instances, generally with one query:

objs = [
    Entry.objects.create(headline='Entry 1'),
    Entry.objects.create(headline='Entry 2'),
]
objs[0].headline = 'This is entry 1'
objs[1].headline = 'This is entry 2'
Entry.objects.bulk_update(objs, ['headline'])

In older versions of Django you could use update() with Case/When, e.g.:

from django.db.models import Case, When

Entry.objects.filter(
    pk__in=headlines  # `headlines` is a pk -> headline mapping
).update(
    headline=Case(*[When(pk=entry_pk, then=headline)
                    for entry_pk, headline in headlines.items()]))