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