[Django] #36492: Sqlite: lack of specificity when querying against booleans hurts the query-optimizer

[Django]

#36492: Sqlite: lack of specificity when querying against booleans hurts the query-
optimizer
-------------------------------------+-------------------------------------
Reporter: Klaas van Schelven | Type:
| Uncategorized
Status: new | Component:
| Uncategorized
Version: 5.2 | Severity: Normal
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
When doing queries against booleanfields Django generates SQL of the the
shape "WHERE" and "WHERE NOT" rather than matching exactly on 1 and 0.
This makes it harder than necessary for the sqlite query optimizer to
optimize, because the selection appears much more broad than it is in
practice.

This is exactly like described in this issue which was acknowledged and
fixed years ago. (though I don't know about the "regression" bit, it's
been going on since at least django 4.2):

https://code.djangoproject.com/ticket/32691 "Performance regression in
Exact lookup on BooleanField on MySQL."

Here's a reproducer:

https://github.com/bugsink/zeroforfalse

{{{

$ python manage.py print_zero_or_false
SELECT "myapp_mymodel"."id", "myapp_mymodel"."boolean_field" FROM
"myapp_mymodel" WHERE NOT "myapp_mymodel"."boolean_field"
SELECT "myapp_mymodel"."id", "myapp_mymodel"."boolean_field" FROM
"myapp_mymodel" WHERE "myapp_mymodel"."boolean_field"

}}}


Here's the context of discovery of this bug, as well as a workaround:
https://github.com/bugsink/bugsink/pull/139
--
Ticket URL: <https://code.djangoproject.com/ticket/36492>
Django <https://code.djangoproject.com/>
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[Django]

#36492: Sqlite: lack of specificity when querying against booleans hurts the query-
optimizer
-------------------------------------+-------------------------------------

Reporter: Klaas van Schelven | Owner: Simon
| Charette
Type: Bug | Status: assigned
Component: Database layer | Version: 5.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted

Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------

Changes (by Simon Charette):

* component: Uncategorized => Database layer (models, ORM)
* owner: (none) => Simon Charette
* stage: Unreviewed => Accepted
* status: new => assigned
* type: Uncategorized => Bug

Comment:

Managed to reproduce as well

{{{#!sql
sqlite> CREATE TABLE foo (a int, b int);
sqlite> CREATE INDEX some_idx ON foo (a, b);
sqlite> EXPLAIN SELECT * FROM foo WHERE NOT a AND NOT b;
addr opcode p1 p2 p3 p4 p5 comment
---- ------------- ---- ---- ---- ------------- -- -------------
0 Init 0 13 0 0 Start at 13
1 OpenRead 0 2 0 2 0 root=2 iDb=0;
foo
2 Explain 2 0 0 SCAN foo 0
3 Rewind 0 12 0 0
4 Column 0 0 1 0 r[1]=foo.a
5 If 1 11 1 0
6 Column 0 1 1 0 r[1]=foo.b
7 If 1 11 1 0
8 Column 0 0 2 0 r[2]=foo.a
9 Column 0 1 3 0 r[3]=foo.b
10 ResultRow 2 2 0 0 output=r[2..3]
11 Next 0 4 0 1
12 Halt 0 0 0 0
13 Transaction 0 0 2 0 1
usesStmtJournal=0
14 Goto 0 1 0 0
sqlite> EXPLAIN SELECT * FROM foo WHERE a=false AND b=false;
addr opcode p1 p2 p3 p4 p5 comment
---- ------------- ---- ---- ---- ------------- -- -------------
0 Init 0 12 0 0 Start at 12
1 OpenRead 1 3 0 k(3,,,) 2 root=3 iDb=0;
some_idx
2 Explain 2 0 0 SEARCH foo USING COVERING INDEX
some_idx (a=? AND b=?) 0
3 Integer 0 1 0 0 r[1]=0
4 Integer 0 2 0 0 r[2]=0
5 SeekGE 1 11 1 2 0 key=r[1..2]
6 IdxGT 1 11 1 2 0 key=r[1..2]
7 Column 1 0 3 0 r[3]=foo.a
8 Column 1 1 4 0 r[4]=foo.b
9 ResultRow 3 2 0 0 output=r[3..4]
10 Next 1 6 1 0
11 Halt 0 0 0 0
12 Transaction 0 0 2 0 1
usesStmtJournal=0
13 Goto 0 1 0 0
}}}

(notice how the NOT usage doesn't make use of the covering index)

Unfortunately Django doesn't have a `has_native_boolean_field` feature
flag so the closest we could do here is override
`conditional_expression_supported_in_where_clause` like we did in #32691.

I'll try to submit work that unifies the different code path we have in
place today.
--
Ticket URL: <https://code.djangoproject.com/ticket/36492#comment:1>

[Django]

#36492: Sqlite: lack of specificity when querying against booleans hurts the query-
optimizer
-------------------------------------+-------------------------------------
Reporter: Klaas van Schelven | Owner: Simon
| Charette
Type: Bug | Status: assigned
Component: Database layer | Version: 5.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted

Has patch: 1 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Simon Charette):

* has_patch: 0 => 1

Comment:

Took the `has_native_boolean_type` approach as suggested on
ticket:32691#comment:8
--
Ticket URL: <https://code.djangoproject.com/ticket/36492#comment:2>

[Django]

#36492: Sqlite: lack of specificity when querying against booleans hurts the query-
optimizer
-------------------------------------+-------------------------------------
Reporter: Klaas van Schelven | Owner: Simon
| Charette
Type: Bug | Status: assigned
Component: Database layer | Version: 5.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 1

Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Simon Charette):

* needs_better_patch: 0 => 1

--
Ticket URL: <https://code.djangoproject.com/ticket/36492#comment:3>

[Django]

#36492: Sqlite: lack of specificity when querying against booleans hurts the query-
optimizer
-------------------------------------+-------------------------------------
Reporter: Klaas van Schelven | Owner: Simon
| Charette
Type: Bug | Status: assigned
Component: Database layer | Version: 5.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0

Needs tests: 0 | Patch needs improvement: 0

Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Simon Charette):

* needs_better_patch: 1 => 0

--
Ticket URL: <https://code.djangoproject.com/ticket/36492#comment:4>