75 lines
2 KiB
Ruby
75 lines
2 KiB
Ruby
|
# frozen_string_literal: true
|
||
|
|
|
||
|
|
module Gitlab
|
||
|
|
# UpdatedNotesPaginator implements a rudimentary form of keyset pagination on
|
||
|
|
# top of a notes relation that has been initialized with a `last_fetched_at`
|
||
|
|
# value. This class will attempt to limit the number of notes returned, and
|
||
|
|
# specify a new value for `last_fetched_at` that will pick up where the last
|
||
|
|
# page of notes left off.
|
||
|
|
class UpdatedNotesPaginator
|
||
|
|
LIMIT = 50
|
||
|
|
MICROSECOND = 1_000_000
|
||
|
|
|
||
|
|
attr_reader :next_fetched_at, :notes
|
||
|
|
|
||
|
|
def initialize(relation, last_fetched_at:)
|
||
|
|
@last_fetched_at = last_fetched_at
|
||
|
|
@now = Time.current
|
||
|
|
|
||
|
|
notes, more = fetch_page(relation)
|
||
|
|
if more
|
||
|
|
init_middle_page(notes)
|
||
|
|
else
|
||
|
|
init_final_page(notes)
|
||
|
|
end
|
||
|
|
end
|
||
|
|
|
||
|
|
def metadata
|
||
|
|
{ last_fetched_at: next_fetched_at_microseconds, more: more }
|
||
|
|
end
|
||
|
|
|
||
|
|
private
|
||
|
|
|
||
|
|
attr_reader :last_fetched_at, :more, :now
|
||
|
|
|
||
|
|
def next_fetched_at_microseconds
|
||
|
|
(next_fetched_at.to_i * MICROSECOND) + next_fetched_at.usec
|
||
|
|
end
|
||
|
|
|
||
|
|
def fetch_page(relation)
|
||
|
|
relation = relation.by_updated_at
|
||
|
|
notes = relation.at_most(LIMIT + 1).to_a
|
||
|
|
|
||
|
|
return [notes, false] unless notes.size > LIMIT
|
||
|
|
|
||
|
|
marker = notes.pop # Remove the marker note
|
||
|
|
|
||
|
|
# Although very unlikely, it is possible that more notes with the same
|
||
|
|
# updated_at may exist, e.g., if created in bulk. Add them all to the page
|
||
|
|
# if this is detected, so pagination won't get stuck indefinitely
|
||
|
|
if notes.last.updated_at == marker.updated_at
|
||
|
|
notes += relation
|
||
|
|
.with_updated_at(marker.updated_at)
|
||
|
|
.id_not_in(notes.map(&:id))
|
||
|
|
.to_a
|
||
|
|
end
|
||
|
|
|
||
|
|
[notes, true]
|
||
|
|
end
|
||
|
|
|
||
|
|
def init_middle_page(notes)
|
||
|
|
@more = true
|
||
|
|
|
||
|
|
# The fetch overlap can be ignored if we're in an intermediate page.
|
||
|
|
@next_fetched_at = notes.last.updated_at + NotesFinder::FETCH_OVERLAP
|
||
|
|
@notes = notes
|
||
|
|
end
|
||
|
|
|
||
|
|
def init_final_page(notes)
|
||
|
|
@more = false
|
||
|
|
@next_fetched_at = now
|
||
|
|
@notes = notes
|
||
|
|
end
|
||
|
|
end
|
||
|
|
end
|