Ordering

[itimky]

There are cases when row-level deadlocks occur on simultaneous update, celery task & Django view for instance.
If update order is preserved (order by pk) there are no more deadlocks.
Implemented via CTE.
Added "ordered=False" for backward compatibility & keep overhead away if ordering not needed.

[mkomitee]

I'm not sure that it matters much at this point, but this only ensures sorting within batches, so if you use the batch feature you're still exposed to the potential for deadlocks.

[itimky]

Correct, but it's possible to sort your data before passing it to bulk_update, so the sorting order will be preserved across all batches.