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Fix performance issue by using LATERAL in group notification CTE (#31123)

pull/2796/head^2
Claire 2024-07-24 20:59:15 +02:00 committed by GitHub
parent 06f070d86d
commit 3a49687ca0
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1 changed files with 40 additions and 38 deletions
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78
app/models/notification.rb
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@ -138,31 +138,51 @@ class Notification < ApplicationRecord
end
end
def paginate_groups(limit, pagination_order)
raise ArgumentError unless %i(asc desc).include?(pagination_order)
query = reorder(id: pagination_order)
unscoped
.with_recursive(
grouped_notifications: [
# Base case: fetching one notification and annotating it with visited groups
query
.select('notifications.*', "ARRAY[COALESCE(notifications.group_key, 'ungrouped-' || notifications.id)] AS groups")
.limit(1),
# Recursive case, always yielding at most one annotated notification
unscoped
.from(
[
# Expose the working table as `wt`, but quit early if we've reached the limit
unscoped
.select('id', 'groups')
.from('grouped_notifications')
.where('array_length(grouped_notifications.groups, 1) < :limit', limit: limit)
.arel.as('wt'),
# Recursive query, using `LATERAL` so we can refer to `wt`
query
.where(pagination_order == :desc ? 'notifications.id < wt.id' : 'notifications.id > wt.id')
.where.not("COALESCE(notifications.group_key, 'ungrouped-' || notifications.id) = ANY(wt.groups)")
.limit(1)
.arel.lateral('notifications'),
]
)
.select('notifications.*', "array_append(wt.groups, COALESCE(notifications.group_key, 'ungrouped-' || notifications.id))"),
]
)
.from('grouped_notifications AS notifications')
.order(id: pagination_order)
.limit(limit)
end
# This returns notifications from the request page, but with at most one notification per group.
# Notifications that have no `group_key` each count as a separate group.
def paginate_groups_by_max_id(limit, max_id: nil, since_id: nil)
query = reorder(id: :desc)
query = query.where(id: ...max_id) if max_id.present?
query = query.where(id: (since_id + 1)...) if since_id.present?
unscoped
.with_recursive(
grouped_notifications: [
query
.select('notifications.*', "ARRAY[COALESCE(notifications.group_key, 'ungrouped-' || notifications.id)] AS groups")
.limit(1),
query
.joins('CROSS JOIN grouped_notifications')
.where('array_length(grouped_notifications.groups, 1) < :limit', limit: limit)
.where('notifications.id < grouped_notifications.id')
.where.not("COALESCE(notifications.group_key, 'ungrouped-' || notifications.id) = ANY(grouped_notifications.groups)")
.select('notifications.*', "array_append(grouped_notifications.groups, COALESCE(notifications.group_key, 'ungrouped-' || notifications.id))")
.limit(1),
]
)
.from('grouped_notifications AS notifications')
.order(id: :desc)
.limit(limit)
query.paginate_groups(limit, :desc)
end
# Differs from :paginate_groups_by_max_id in that it gives the results immediately following min_id,
@ -172,25 +192,7 @@ class Notification < ApplicationRecord
query = reorder(id: :asc)
query = query.where(id: (min_id + 1)...) if min_id.present?
query = query.where(id: ...max_id) if max_id.present?
unscoped
.with_recursive(
grouped_notifications: [
query
.select('notifications.*', "ARRAY[COALESCE(notifications.group_key, 'ungrouped-' || notifications.id)] AS groups")
.limit(1),
query
.joins('CROSS JOIN grouped_notifications')
.where('array_length(grouped_notifications.groups, 1) < :limit', limit: limit)
.where('notifications.id > grouped_notifications.id')
.where.not("COALESCE(notifications.group_key, 'ungrouped-' || notifications.id) = ANY(grouped_notifications.groups)")
.select('notifications.*', "array_append(grouped_notifications.groups, COALESCE(notifications.group_key, 'ungrouped-' || notifications.id))")
.limit(1),
]
)
.from('grouped_notifications AS notifications')
.order(id: :asc)
.limit(limit)
query.paginate_groups(limit, :asc)
end
def to_a_grouped_paginated_by_id(limit, options = {})