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PERF: Reduce ActiveRecord allocations in `CategoryList#find_relevant_topics` (#25950) 

Why this change?

Prior to this change, the `CategoryList#find_relevant_topics` method was
loading and allocating all `CategoryFeaturedTopic` records in the
database to eventually only just use its `category_id` and `topic_id`
column. On a site with many `CategoryFeaturedTopic` records, the loading
of the ActiveRecord objects is a source of bottleneck.

The other problem with the `CategoryList#find_relevant_topics` method is
that it is unconditionally loading all records from the database even if
the user does not have access to the category. This again is wasteful.

What does this change do?

This commit makes it such that `CategoryList#find_relevant_topics` is
called only after `CategoryList#find_categories` in the `CategoryList#initialize`
method so that we can filter featured topics against categories that the
user has access to.

The second change is that Instead of loading `CategoryFeaturedTopic` records, we make an
inner join agains the `topics` table instead and skip any allocation of
`CatgoryFeaturedTopic` ActiveRecord objects.
This commit is contained in:
Alan Guo Xiang Tan 2024-02-29 12:19:04 +08:00 committed by GitHub
parent 120a2f70a9
commit f562da3150
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
2 changed files with 39 additions and 46 deletions
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50
app/models/category_list.rb
View File

@ -31,8 +31,8 @@ class CategoryList
@guardian = guardian || Guardian.new
@options = options
find_relevant_topics if options[:include_topics]
find_categories
find_relevant_topics if options[:include_topics]
prune_empty
find_user_data
@ -71,17 +71,18 @@ class CategoryList
private
def find_relevant_topics
@topics_by_id = {}
@topics_by_category_id = {}
category_featured_topics = CategoryFeaturedTopic.select(%i[category_id topic_id]).order(:rank)
@all_topics =
Topic.where(id: category_featured_topics.map(&:topic_id)).includes(
:shared_draft,
:category,
{ topic_thumbnails: %i[optimized_image upload] },
)
Topic
.secured(@guardian)
.joins(
"INNER JOIN category_featured_topics ON topics.id = category_featured_topics.topic_id",
)
.where("category_featured_topics.category_id IN (?)", categories_with_descendants.map(&:id))
.select(
"topics.*, category_featured_topics.category_id AS category_featured_topic_category_id",
)
.includes(:shared_draft, :category, { topic_thumbnails: %i[optimized_image upload] })
.order("category_featured_topics.rank")
@all_topics = @all_topics.joins(:tags).where(tags: { name: @options[:tag] }) if @options[
:tag
@ -103,16 +104,18 @@ class CategoryList
end
@all_topics = TopicQuery.remove_muted_tags(@all_topics, @guardian.user).includes(:last_poster)
featured_topics_by_category_id = Hash.new { |h, k| h[k] = [] }
@all_topics.each do |t|
# hint for the serializer
t.include_last_poster = true
t.dismissed = dismissed_topic?(t)
@topics_by_id[t.id] = t
featured_topics_by_category_id[t.category_featured_topic_category_id] << t
end
category_featured_topics.each do |cft|
@topics_by_category_id[cft.category_id] ||= []
@topics_by_category_id[cft.category_id] << cft.topic_id
categories_with_descendants.each do |category|
category.displayable_topics = featured_topics_by_category_id[category.id]
end
end
@ -213,23 +216,6 @@ class CategoryList
)
category.has_children = category.subcategories.present?
end
if @topics_by_category_id
categories_with_descendants.each do |c|
topics_in_cat = @topics_by_category_id[c.id]
if topics_in_cat.present?
c.displayable_topics = []
topics_in_cat.each do |topic_id|
topic = @topics_by_id[topic_id]
if topic.present? && @guardian.can_see?(topic)
# topic.category is very slow under rails 4.2
topic.association(:category).target = c
c.displayable_topics << topic
end
end
end
end
end
end
def prune_empty

35
spec/models/category_list_spec.rb
View File

@ -27,21 +27,21 @@ RSpec.describe CategoryList do
it "doesn't show topics that you can't view" do
public_cat = Fabricate(:category_with_definition) # public category
Fabricate(:topic, category: public_cat)
topic_in_public_cat = Fabricate(:topic, category: public_cat)
private_cat = Fabricate(:category_with_definition) # private category
Fabricate(:topic, category: private_cat)
topic_in_private_cat = Fabricate(:topic, category: private_cat)
private_cat.set_permissions(admins: :full)
private_cat.save
secret_subcat = Fabricate(:category_with_definition, parent_category_id: public_cat.id) # private subcategory
Fabricate(:topic, category: secret_subcat)
topic_in_secret_subcat = Fabricate(:topic, category: secret_subcat)
secret_subcat.set_permissions(admins: :full)
secret_subcat.save
muted_tag = Fabricate(:tag) # muted tag
SiteSetting.default_tags_muted = muted_tag.name
Fabricate(:topic, category: public_cat, tags: [muted_tag])
topic_in_public_cat_2 = Fabricate(:topic, category: public_cat, tags: [muted_tag])
muted_tag_2 = Fabricate(:tag)
TagUser.create!(
@ -58,16 +58,21 @@ RSpec.describe CategoryList do
.categories
.find { |x| x.name == public_cat.name }
.displayable_topics
.count,
).to eq(3)
.map(&:id),
).to contain_exactly(
topic_in_public_cat.id,
topic_in_secret_subcat.id,
topic_in_public_cat_2.id,
)
expect(
CategoryList
.new(Guardian.new(admin), include_topics: true)
.categories
.find { |x| x.name == private_cat.name }
.displayable_topics
.count,
).to eq(1)
.map(&:id),
).to contain_exactly(topic_in_private_cat.id)
expect(
CategoryList
@ -75,8 +80,9 @@ RSpec.describe CategoryList do
.categories
.find { |x| x.name == public_cat.name }
.displayable_topics
.count,
).to eq(2)
.map(&:id),
).to contain_exactly(topic_in_public_cat.id, topic_in_public_cat_2.id)
expect(
CategoryList
.new(Guardian.new(user), include_topics: true)
@ -90,8 +96,9 @@ RSpec.describe CategoryList do
.categories
.find { |x| x.name == public_cat.name }
.displayable_topics
.count,
).to eq(1)
.map(&:id),
).to contain_exactly(topic_in_public_cat.id)
expect(
CategoryList
.new(Guardian.new(nil), include_topics: true)
@ -112,8 +119,8 @@ RSpec.describe CategoryList do
.categories
.find { |x| x.name == cat.name }
.displayable_topics
.count,
).to eq(1)
.map(&:id),
).to contain_exactly(topic.id)
TopicUser.change(user.id, topic.id, notification_level: TopicUser.notification_levels[:muted])