#33973: Performance regression when moving from 3.1 to 3.2
-------------------------------------+-------------------------------------
Reporter: Marc Parizeau | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 3.2
Severity: Normal | Resolution:
Keywords: performance | Triage Stage:
regression | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Marc Parizeau):
Here is the "explanation" for Django 4.0.7:
{{{
time 0.3011052919999955
Sort (cost=62.30..62.31 rows=1 width=1207)
Sort Key: content_course.uid, content_version.start DESC
-> Nested Loop Left Join (cost=0.41..62.29 rows=1 width=1207)
-> Nested Loop Left Join (cost=0.28..40.58 rows=1 width=1202)
-> Nested Loop (cost=0.14..39.68 rows=1 width=1124)
-> Seq Scan on content_teacher (cost=0.00..7.65
rows=1 width=8)
Filter: (user_id = 59)
-> Index Scan using content_semester_pkey on
content_content (cost=0.14..28.99 rows=1 width=1124)
Index Cond: (id = content_teacher.content_id)
Filter: ((id <> 58) AND GREATEST((SubPlan 3),
false))
SubPlan 3
-> Nested Loop Anti Join
(cost=0.43..18547.19 rows=909 width=0)
-> Seq Scan on forum_thread v0_1
(cost=0.00..1799.79 rows=1174 width=8)
Filter: (content_id =
content_content.id)
-> Index Only Scan using
forum_threadentry_thread_id_user_id_cd21c4a5_uniq on forum_threadentry
u1_1 (cost=0.43..55.66 rows=33 width=8)
Index Cond: ((thread_id = v0_1.id)
AND (user_id = 59))
-> Index Scan using content_course_pkey on content_course
(cost=0.14..0.82 rows=1 width=86)
Index Cond: (id = content_content.course_id)
-> Index Scan using content_version_pkey on content_version
(cost=0.14..0.82 rows=1 width=12)
Index Cond: (id = content_content.version_id)
SubPlan 1
-> Nested Loop Anti Join (cost=0.43..18547.19 rows=909
width=0)
-> Seq Scan on forum_thread v0 (cost=0.00..1799.79
rows=1174 width=8)
Filter: (content_id = content_content.id)
-> Index Only Scan using
forum_threadentry_thread_id_user_id_cd21c4a5_uniq on forum_threadentry u1
(cost=0.43..55.66 rows=33 width=8)
Index Cond: ((thread_id = v0.id) AND (user_id = 59))
}}}
And the corresponding SQL:
{{{
SELECT "content_content"."id", "content_content"."created",
"content_content"."description", "content_content"."disabled",
"content_content"."modified", "content_content"."objectives",
"content_content"."published", "content_content"."title",
"content_content"."course_id", "content_content"."version_id",
"content_content"."exercise_weight", "content_content"."midterm_weight",
"content_content"."final_weight", "content_content"."project_weight",
"content_content"."forum_weight", "content_content"."welcome_video",
"content_content"."navigate_video", "content_content"."forum_video",
"content_content"."lambda_fct_id", "content_content"."dl_key_version",
"content_content"."dl_key_token", "content_content"."exam_key_token",
"content_content"."lectures_url", GREATEST(EXISTS(SELECT (1) AS "a" FROM
"forum_thread" V0 WHERE (V0."content_id" = ("content_content"."id") AND
NOT (EXISTS(SELECT (1) AS "a" FROM "forum_threadentry" U1 WHERE
(U1."user_id" = 59 AND U1."thread_id" = (V0."id")) LIMIT 1))) LIMIT 1),
False) AS "unread" FROM "content_content" INNER JOIN "content_teacher" ON
("content_content"."id" = "content_teacher"."content_id") LEFT OUTER JOIN
"content_course" ON ("content_content"."course_id" =
"content_course"."id") LEFT OUTER JOIN "content_version" ON
("content_content"."version_id" = "content_version"."id") WHERE
("content_teacher"."user_id" = 59 AND NOT ("content_content"."id" = 58)
AND GREATEST(EXISTS(SELECT (1) AS "a" FROM "forum_thread" V0 WHERE
(V0."content_id" = ("content_content"."id") AND NOT (EXISTS(SELECT (1) AS
"a" FROM "forum_threadentry" U1 WHERE (U1."user_id" = 59 AND
U1."thread_id" = (V0."id")) LIMIT 1))) LIMIT 1), False)) ORDER BY
"content_course"."uid" ASC, "content_version"."start" DESC
}}}
As for Django 4.1, I can't do it right now, because I am getting
`Expression contains mixed types: IntegerField, SmallIntegerField` errors
which I haven't been able to remove so far.
But my issues definitely started with Django 3.2, not with Django 4 which
seems to behave similarly for my specific query.
--
Ticket URL: <https://code.djangoproject.com/ticket/33973#comment:4>
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