Fixed #33355 -- Optimized SQLite backend connection functions.

[adamchainz]

ticket-33355

[ngnpope]

Boo! 😄 But, yes, while less elegant, this makes a lot of sense.

It's straightforward. I only had a few minor comments around naming.

A few more thoughts:

• It might be worth moving all these _sqlite_* functions into a separate module to decruft base.py, maybe a private django.db.backends.sqlite._functions module?
• If in a separate module, we could do from math import ... and remove the attribute lookup in each function for another little speed boost?
• Maybe that module could also contain a register(connection) function so we can move all of the registration out of base.py?

[adamchainz]

It might be worth moving all these _sqlite_* functions into a separate module to decruft base.py, maybe a private django.db.backends.sqlite._functions module?

Yes I will give that a try.

If in a separate module, we could do from math import ... and remove the attribute lookup in each function for another little speed boost?

And that!

Maybe that module could also contain a register(connection) function so we can move all of the registration out of base.py?

Yes.

[ngnpope]

A few follow on comments...

...and then, as this issue is about optimising these functions, I couldn't resist doing a more thorough review of these as they're being moved around anyway. Seems like a good opportunity to eke out some more improvements.

Aside from the comments below, could you also group the _sqlite_*_extract() functions together, and the _sqlite_*_trunc(), etc., etc.

[adamchainz]

I extracted the changes to the trunc functions with the bug fix into #15182 , which should be merged first. Then I will rebuild this PR as a new series of commits with fewer steps.

[ngnpope]

@adamchainz Could you rebase this one now that #15182 has landed? Then I'll give it another look through.

[adamchainz]

I've rebuilt the branch as a new series of commits. I think I managed to capture everything.

[ngnpope]

Thanks Adam, this looks great! 🌟

Also thanks for humouring me with looking through for little tweaks. When shifting a bunch of stuff around like this it's worth making sure we get the maximum benefit while we're in the area.

[felixxm]

@adamchainz Thanks 👍

I merged the first two commits in a8fa3e5 and c4328c2.

[felixxm]

Suggested change

	# typecast_timestamp returns a date or a datetime without timezone.
	# typecast_timestamp() returns a date or a datetime without timezone.

[felixxm]

I merged LPad() optimization in fa4b2c1.

[felixxm]

Thanks both 🥇

I reorganized commits.

[adamchainz]

Okay, looks good!

[adamchainz]

Yyyyyyeah