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# 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.order_updated_asc.with_order_id_asc
notes = relation.limit(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
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