Aggregating save()s in Django?


Question

I'm using Django with an sqlite backend, and write performance is a problem. I may graduate to a "proper" db at some stage, but for the moment I'm stuck with sqlite. I think that my write performance problems are probably related to the fact that I'm creating a large number of rows, and presumably each time I save() one it's locking, unlocking and syncing the DB on disk.

How can I aggregate a large number of save() calls into a single database operation?

1
41
8/3/2010 9:33:55 AM

Accepted Answer

EDITED: commit_on_success is deprecated and was removed in Django 1.8. Use transaction.atomic instead. See Fraser Harris's answer.

Actually this is easier to do then you think. You can use transactions in Django. These batch database operations (specifically save, insert and delete) into one operation. I've found the easiest one to use is commit_on_success. Essentially you wrap your database save operations into a function and then use the commit_on_success decorator.

from django.db.transaction import commit_on_success

@commit_on_success
def lot_of_saves(queryset):
    for item in queryset:
        modify_item(item)
        item.save()

This will have a huge speed increase. You'll also get the benefit of having roll-backs if any of the items fail. If you have millions of save operations then you may have to commit them in blocks using the commit_manually and transaction.commit() but I've rarely needed that.

Hope that helps,

Will

66
4/10/2019 1:26:33 PM

New as of Django 1.6 is atomic, a simple API to control DB transactions. Copied verbatim from the docs:

atomic is usable both as a decorator:

from django.db import transaction

@transaction.atomic
def viewfunc(request):
    # This code executes inside a transaction.
    do_stuff()

and as a context manager:

from django.db import transaction

def viewfunc(request):
    # This code executes in autocommit mode (Django's default).
    do_stuff()

    with transaction.atomic():
        # This code executes inside a transaction.
        do_more_stuff()

Legacy django.db.transaction functions autocommit(), commit_on_success(), and commit_manually() have been deprecated and will be remove in Django 1.8.


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