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
16759	Expensive sql.Query cloning	Alexander Schepanovski	Alexander Schepanovski	"I dug into `Query.clone()` and found that deepcopying of it's where tree may sometimes lead to deepcopying of model fields and _meta. And with a help of related fields it sometimes becomes a disaster.

I dug further and found that actual culprits are `db.models.sql.where.Constraint` 
and `db.models.sql.expressions.SQLEvaluator` which ""leak"" deepcopying to ORM objects.

We fixed this problem for ourselves and here is the patch."	Bug	closed	Database layer (models, ORM)	1.3	Normal	fixed	orm performance cloning	anssi.kaariainen@… Anssi Kääriäinen hv@… niwi@…	Ready for checkin	1	0	0	0	0	0