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
31275	Optimize MariaDB/MySQL sql_flush	Adam Johnson	Masashi SHIBATA	"This was suggested as an extra feature for Django-MySQL by @jonatron in https://github.com/adamchainz/django-mysql/pull/611/files , but it would make more sense to make it in Django core.

Currently MySQL's sql_flush emits TRUNCATE TABLE statements. These are relatively slow on small tables since they force recreation of the table on disk. The alternative, `DELETE FROM`, is faster. I can see a diference even for a single empty table locally (MariaDB 10.4):

{{{
chainz@localhost [21]> truncate t2;
Query OK, 0 rows affected (0.005 sec)

chainz@localhost [22]> delete from t2;
Query OK, 0 rows affected (0.000 sec)
}}}

`TransactionTestCase` uses sql_flush, via the flush management command, to reset the database. Most test suites don't use very large tables, so  using `DELETE FROM` should normally be faster in this case. Optimizing it MySQL to use `DELETE FROM` for flushing, at least for tables up to a certain size (1000 rows or similar heuristic) could save lot of time when using `TransactionTestCase`."	Cleanup/optimization	closed	Database layer (models, ORM)	dev	Normal	fixed		Simon Charette	Ready for checkin	1	0	0	0	0	0