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
17030	Remove special handling of deferred models in queryset iterators	Anssi Kääriäinen	nobody	"Suor gave me a great idea in ticket #17025: use attname cache for `__init__`. This turned out to work really well for deferred models: we don't need to special case them any more in queryset iterator loops (we do of course need to get the right deferred model class still).

Because the model `__init__` did need to get the data in the same order as the model._meta.fields for *args based initialization, we couldn't use the fast init for deferred models. But if the model's options know the selected columns in the queryset, we suddenly can use the *args based `__init__` which is a lot faster. A new model._meta.get_init_attnames() method was added for this.

One might wonder if this is backwards compatible. Well, the `__init__` behaviour surely changed for deferred models, but I don't think this matters: the deferred classes are only for internal use of querysets, and thus the user should never call `__init__` of deferred models directly.

The speedup from djangobench for raw_deferred is 2.5x. The speedup for query_all and query_all_multifield is about 1.05. There isn't a djangobench test for .defer, but according to my test .only('id')[0] is about 2x faster, and .only('id)[0:100] is about 1.6x faster.

The attached patch passes all test. There is some cleanup needed in get_cached_row, but there is a separate patch for optimizing those parts of the queryset, so I didn't bother to clean it up. However there is something strange going on with select_related querysets and its handling of load_fields. It seems that sometimes the field is passed as field.attname and sometimes as field.name to deferred_model_factory, and I don't believe that to be correct. The patch just checks for both, but that is the wrong cure. I believe the load_fields should always be field.name, not field.attname. Another tickets problem IMHO.

Suor also suggested the idea of using `__dict__`.update in model.`__init__`. That would speed up model initialization somewhat, but I believe that is backwards incompatible as `__setattr__` would not be called. Is this corret? We are talking about 10-15% speed increase in the case the model has a lot of columns."	Cleanup/optimization	closed	Database layer (models, ORM)	1.3	Normal	wontfix		anssi.kaariainen@…	Accepted	1	0	0	0	0	0