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Merge branch 'jprovazn-fix-positioning' into 'master' 

Optimize  relative re-positioning

See merge request gitlab-org/gitlab-ce!30938
This commit is contained in:
Sean McGivern 2019-08-05 10:56:25 +00:00
parent 5f4eb3d5e5 3f9b1ecdb3
commit ff76ca4494
5 changed files with 169 additions and 79 deletions
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113
app/models/concerns/relative_positioning.rb
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@ -29,10 +29,6 @@ module RelativePositioning
MAX_POSITION = Gitlab::Database::MAX_INT_VALUE
IDEAL_DISTANCE = 500
included do
after_save :save_positionable_neighbours
end
class_methods do
def move_nulls_to_end(objects)
objects = objects.reject(&:relative_position)
@ -114,11 +110,12 @@ module RelativePositioning
return move_after(before) unless after
return move_before(after) unless before
# If there is no place to insert an item we need to create one by moving the before item closer
# to its predecessor. This process will recursively move all the predecessors until we have a place
# If there is no place to insert an item we need to create one by moving the item
# before this and all preceding items until there is a gap
before, after = after, before if after.relative_position < before.relative_position
if (after.relative_position - before.relative_position) < 2
before.move_before
@positionable_neighbours = [before] # rubocop:disable Gitlab/ModuleWithInstanceVariables
after.move_sequence_before
before.reset
end
self.relative_position = self.class.position_between(before.relative_position, after.relative_position)
@ -128,12 +125,8 @@ module RelativePositioning
pos_before = before.relative_position
pos_after = before.next_relative_position
if before.shift_after?
item_to_move = self.class.relative_positioning_query_base(self).find_by!(relative_position: pos_after)
item_to_move.move_after
@positionable_neighbours = [item_to_move] # rubocop:disable Gitlab/ModuleWithInstanceVariables
pos_after = item_to_move.relative_position
if pos_after && (pos_after - pos_before) < 2
before.move_sequence_after
end
self.relative_position = self.class.position_between(pos_before, pos_after)
@ -143,12 +136,8 @@ module RelativePositioning
pos_after = after.relative_position
pos_before = after.prev_relative_position
if after.shift_before?
item_to_move = self.class.relative_positioning_query_base(self).find_by!(relative_position: pos_before)
item_to_move.move_before
@positionable_neighbours = [item_to_move] # rubocop:disable Gitlab/ModuleWithInstanceVariables
pos_before = item_to_move.relative_position
if pos_before && (pos_after - pos_before) < 2
after.move_sequence_before
end
self.relative_position = self.class.position_between(pos_before, pos_after)
@ -162,36 +151,82 @@ module RelativePositioning
self.relative_position = self.class.position_between(min_relative_position || START_POSITION, MIN_POSITION)
end
# Indicates if there is an item that should be shifted to free the place
def shift_after?
next_pos = next_relative_position
next_pos && (next_pos - relative_position) == 1
# Moves the sequence before the current item to the middle of the next gap
# For example, we have 5 11 12 13 14 15 and the current item is 15
# This moves the sequence 11 12 13 14 to 8 9 10 11
def move_sequence_before
next_gap = find_next_gap_before
delta = optimum_delta_for_gap(next_gap)
move_sequence(next_gap[:start], relative_position, -delta)
end
# Indicates if there is an item that should be shifted to free the place
def shift_before?
prev_pos = prev_relative_position
prev_pos && (relative_position - prev_pos) == 1
# Moves the sequence after the current item to the middle of the next gap
# For example, we have 11 12 13 14 15 21 and the current item is 11
# This moves the sequence 12 13 14 15 to 15 16 17 18
def move_sequence_after
next_gap = find_next_gap_after
delta = optimum_delta_for_gap(next_gap)
move_sequence(relative_position, next_gap[:start], delta)
end
private
# rubocop:disable Gitlab/ModuleWithInstanceVariables
def save_positionable_neighbours
return unless @positionable_neighbours
# Supposing that we have a sequence of items: 1 5 11 12 13 and the current item is 13
# This would return: `{ start: 11, end: 5 }`
def find_next_gap_before
items_with_next_pos = scoped_items
.select('relative_position AS pos, LEAD(relative_position) OVER (ORDER BY relative_position DESC) AS next_pos')
.where('relative_position <= ?', relative_position)
.order(relative_position: :desc)
status = @positionable_neighbours.all? { |item| item.save(touch: false) }
@positionable_neighbours = nil
status
find_next_gap(items_with_next_pos).tap do |gap|
gap[:end] ||= MIN_POSITION
end
end
# Supposing that we have a sequence of items: 13 14 15 20 24 and the current item is 13
# This would return: `{ start: 15, end: 20 }`
def find_next_gap_after
items_with_next_pos = scoped_items
.select('relative_position AS pos, LEAD(relative_position) OVER (ORDER BY relative_position ASC) AS next_pos')
.where('relative_position >= ?', relative_position)
.order(:relative_position)
find_next_gap(items_with_next_pos).tap do |gap|
gap[:end] ||= MAX_POSITION
end
end
def find_next_gap(items_with_next_pos)
gap = self.class.from(items_with_next_pos, :items_with_next_pos)
.where('ABS(pos - next_pos) > 1 OR next_pos IS NULL')
.limit(1)
.pluck(:pos, :next_pos)
.first
{ start: gap[0], end: gap[1] }
end
def optimum_delta_for_gap(gap)
delta = ((gap[:start] - gap[:end]) / 2.0).abs.ceil
[delta, IDEAL_DISTANCE].min
end
def move_sequence(start_pos, end_pos, delta)
scoped_items
.where.not(id: self.id)
.where('relative_position BETWEEN ? AND ?', start_pos, end_pos)
.update_all("relative_position = relative_position + #{delta}")
end
# rubocop:enable Gitlab/ModuleWithInstanceVariables
def calculate_relative_position(calculation)
# When calculating across projects, this is much more efficient than
# MAX(relative_position) without the GROUP BY, due to index usage:
# https://gitlab.com/gitlab-org/gitlab-ce/issues/54276#note_119340977
relation = self.class.relative_positioning_query_base(self)
relation = scoped_items
.order(Gitlab::Database.nulls_last_order('position', 'DESC'))
.group(self.class.relative_positioning_parent_column)
.limit(1)
@ -203,4 +238,8 @@ module RelativePositioning
.first&.
last
end
def scoped_items
self.class.relative_positioning_query_base(self)
end
end

5
changelogs/unreleased/jprovazn-fix-positioning.yml Normal file
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@ -0,0 +1,5 @@
---
title: Optimize relative re-positioning when moving issues.
merge_request: 30938
author:
type: fixed

24
db/migrate/20190802012622_reorder_issues_project_id_relative_position_index.rb Normal file
View File

@ -0,0 +1,24 @@
# frozen_string_literal: true
class ReorderIssuesProjectIdRelativePositionIndex < ActiveRecord::Migration[5.2]
include Gitlab::Database::MigrationHelpers
DOWNTIME = false
disable_ddl_transaction!
OLD_INDEX_NAME = 'index_issues_on_project_id_and_state_and_rel_position_and_id'
NEW_INDEX_NAME = 'index_issues_on_project_id_and_rel_position_and_state_and_id'
def up
add_concurrent_index :issues, [:project_id, :relative_position, :state, :id], order: { id: :desc }, name: NEW_INDEX_NAME
remove_concurrent_index_by_name :issues, OLD_INDEX_NAME
end
def down
add_concurrent_index :issues, [:project_id, :state, :relative_position, :id], order: { id: :desc }, name: OLD_INDEX_NAME
remove_concurrent_index_by_name :issues, NEW_INDEX_NAME
end
end

4
db/schema.rb
View File

@ -10,7 +10,7 @@
#
# It's strongly recommended that you check this file into your version control system.
ActiveRecord::Schema.define(version: 2019_08_01_114109) do
ActiveRecord::Schema.define(version: 2019_08_02_012622) do
# These are extensions that must be enabled in order to support this database
enable_extension "pg_trgm"
@ -1716,7 +1716,7 @@ ActiveRecord::Schema.define(version: 2019_08_01_114109) do
t.index ["project_id", "created_at", "id", "state"], name: "index_issues_on_project_id_and_created_at_and_id_and_state"
t.index ["project_id", "due_date", "id", "state"], name: "idx_issues_on_project_id_and_due_date_and_id_and_state_partial", where: "(due_date IS NOT NULL)"
t.index ["project_id", "iid"], name: "index_issues_on_project_id_and_iid", unique: true
t.index ["project_id", "state", "relative_position", "id"], name: "index_issues_on_project_id_and_state_and_rel_position_and_id", order: { id: :desc }
t.index ["project_id", "relative_position", "state", "id"], name: "index_issues_on_project_id_and_rel_position_and_state_and_id", order: { id: :desc }
t.index ["project_id", "updated_at", "id", "state"], name: "index_issues_on_project_id_and_updated_at_and_id_and_state"
t.index ["relative_position"], name: "index_issues_on_relative_position"
t.index ["state"], name: "index_issues_on_state"

102
spec/support/shared_examples/relative_positioning_shared_examples.rb
View File

@ -9,6 +9,12 @@ RSpec.shared_examples 'a class that supports relative positioning' do
create(factory, params.merge(default_params))
end
def create_items_with_positions(positions)
positions.map do |position|
create_item(relative_position: position)
end
end
describe '.move_nulls_to_end' do
it 'moves items with null relative_position to the end' do
skip("#{item1} has a default relative position") if item1.relative_position
@ -104,46 +110,6 @@ RSpec.shared_examples 'a class that supports relative positioning' do
end
end
describe '#shift_after?' do
before do
[item1, item2].each do |item1|
item1.move_to_end && item1.save
end
end
it 'returns true' do
item1.update(relative_position: item2.relative_position - 1)
expect(item1.shift_after?).to be_truthy
end
it 'returns false' do
item1.update(relative_position: item2.relative_position - 2)
expect(item1.shift_after?).to be_falsey
end
end
describe '#shift_before?' do
before do
[item1, item2].each do |item1|
item1.move_to_end && item1.save
end
end
it 'returns true' do
item1.update(relative_position: item2.relative_position + 1)
expect(item1.shift_before?).to be_truthy
end
it 'returns false' do
item1.update(relative_position: item2.relative_position + 2)
expect(item1.shift_before?).to be_falsey
end
end
describe '#move_between' do
before do
[item1, item2].each do |item1|
@ -257,5 +223,61 @@ RSpec.shared_examples 'a class that supports relative positioning' do
expect(new_item.relative_position).to be(100)
end
it 'avoids N+1 queries when rebalancing other items' do
items = create_items_with_positions([100, 101, 102])
count = ActiveRecord::QueryRecorder.new do
new_item.move_between(items[-2], items[-1])
end
items = create_items_with_positions([150, 151, 152, 153, 154])
expect { new_item.move_between(items[-2], items[-1]) }.not_to exceed_query_limit(count)
end
end
describe '#move_sequence_before' do
it 'moves the whole sequence of items to the middle of the nearest gap' do
items = create_items_with_positions([90, 100, 101, 102])
items.last.move_sequence_before
items.last.save!
positions = items.map { |item| item.reload.relative_position }
expect(positions).to eq([90, 95, 96, 102])
end
it 'finds a gap if there are unused positions' do
items = create_items_with_positions([100, 101, 102])
items.last.move_sequence_before
items.last.save!
positions = items.map { |item| item.reload.relative_position }
expect(positions).to eq([50, 51, 102])
end
end
describe '#move_sequence_after' do
it 'moves the whole sequence of items to the middle of the nearest gap' do
items = create_items_with_positions([100, 101, 102, 110])
items.first.move_sequence_after
items.first.save!
positions = items.map { |item| item.reload.relative_position }
expect(positions).to eq([100, 105, 106, 110])
end
it 'finds a gap if there are unused positions' do
items = create_items_with_positions([100, 101, 102])
items.first.move_sequence_after
items.first.save!
positions = items.map { |item| item.reload.relative_position }
expect(positions).to eq([100, 601, 602])
end
end
end