Document that bulk update is available in Django 2.2

[aykut]

Document that bulk update is available in Django 2.2

[ses4j]

@orf @Ehco1996 Django 2.2 is now released, and docs are no longer draft:

https://docs.djangoproject.com/en/2.2/ref/models/querysets/#django.db.models.query.QuerySet.bulk_update

[orf]

I'd like to really thank you for creating a reproduction repository @mikicz, it's increadibly helpful and I wish everyones reproductions where as detailed as this!

I've created a ticket on the Django bugtracker (https://code.djangoproject.com/ticket/31202) and assigned it to myself. I'm somewhat busy right now but I promise that I will spend some time and see if I can dig more into this. I'll update the ticket rather than this issue.

Thanks again for creating this test case.

[Ehco1996]

it's so great ,but i found that the doc is in dev ,and the newest django stable ver is 2.1.2
so bulk_update is not available

[wahello]

Thanks a great. It's helpful before django 2.2.

[mikicz]

It would also be really helpful to document the speed difference. In my experience (updating tens of thousands of lines) this package does the update waaay faster.

[orf]

Can you elaborate? It uses the same method, so the speed difference should be negligible. If you find Django is way slower then please open a ticket with some details!

[mikicz]

I'm on Django 2.2.9. Might be doing something wrong, but can't see what.

objects = list(Model.objects.all()[:10000])
Model.objects.bulk_update(
    objects,
    [], # about 10 fields
    batch_size=1000
)

from bulk_update.helper import bulk_update

objects = list(Model.objects.all()[:10000])
bulk_update(
    objects,
    update_fields=[], # about 10 fields
    batch_size=1000
)

Bellow is profiling done by pyinstrument. Django in-built solution takes 144 seconds on my pc. The package one takes 2.5 seconds.

inbuilt_pyinstrument.txt
package_pyinstrument.txt

[mikicz]

@orf Hi, did you manage to to take a look at that? I could provide a more comprehensive example if necessary...

[orf]

Not yet, but those samples are invaluable. The two big differences between this package and the Django inbuilt one are:

1. Django uses the Expressions API. This is where the overhead is coming from - but it's pretty ridiculous one. Perhaps you're hitting an edge case here.
2. Django works around SQL parameter limitations in some databases (Oracle/SQlite).

Knowing the types of the fields would be really useful, as well as the kinds of values those fields contain (lots of large strings or arrays?).

I would love it if you could perhaps post the timings here with 1 to 10 columns, and the same number of rows. It would be interesting to see how the times grow?

[mikicz]

I created an example project. Please excuse the non-imaginative naming of my classes and columns. The column types respect the types of my model in the project where I encountered the problem. In the project I have there are a bunch of other columns as well which aren't updated, I didn't include them, but obviously that isn't what's causing the slow performance, as the results bellow show. https://github.com/mikicz/bulk-update-tests

The most important bits:
Models: https://github.com/mikicz/bulk-update-tests/blob/master/apps/something/models.py
Update code: https://github.com/mikicz/bulk-update-tests/blob/master/apps/something/test_bulk_update.py

Results on my new quite powerfull Dell, with local PostgreSQL 11.5

In [1]: Something.objects.count()                                                                                                                                                                                                             
Out[1]: 1008895

In [2]: from apps.something.test_bulk_update import *                                                                                                                                                                                         

In [3]: %time inbuilt()                                                                                                                                                                                                                       
CPU times: user 2min 9s, sys: 653 ms, total: 2min 10s
Wall time: 2min 24s

In [4]: %time bulk_update_package()                                                                                                                                                                                                           
CPU times: user 11.2 s, sys: 41.6 ms, total: 11.3 s
Wall time: 24.2 s

I would say that the difference is quite significant. I am planning to do some more analysis, maybe dropping some of the different column types from the update etc.

[mikicz]

I'm only happy to be of help, to be a tiny part of making Django such a great resource for everybody using it. Thank you for your work and actioning this!