Merge branch '329357-move-rebalancing-outside-transaction' into 'master'

Rebalance without transaction

See merge request gitlab-org/gitlab!68746

app/models/issue.rb

@@ -323,6 +323,13 @@ class Issue < ApplicationRecord
     )
   end
 
+  def self.column_order_id_asc
+    Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
+      attribute_name: 'id',
+      order_expression: arel_table[:id].asc
+    )
+  end
+
   def self.to_branch_name(*args)
     branch_name = args.map(&:to_s).each_with_index.map do |arg, i|
       arg.parameterize(preserve_case: i == 0).presence

app/models/project.rb

@@ -526,6 +526,7 @@ class Project < ApplicationRecord
   scope :sorted_by_stars_desc, -> { reorder(self.arel_table['star_count'].desc) }
   scope :sorted_by_stars_asc, -> { reorder(self.arel_table['star_count'].asc) }
   # Sometimes queries (e.g. using CTEs) require explicit disambiguation with table name
+  scope :projects_order_id_asc, -> { reorder(self.arel_table['id'].asc) }
   scope :projects_order_id_desc, -> { reorder(self.arel_table['id'].desc) }
 
   scope :sorted_by_similarity_desc, -> (search, include_in_select: false) do

app/services/issue_rebalancing_service.rb

-# frozen_string_literal: true
-
-class IssueRebalancingService
-  MAX_ISSUE_COUNT = 10_000
-  BATCH_SIZE = 100
-  SMALLEST_BATCH_SIZE = 5
-  RETRIES_LIMIT = 3
-  TooManyIssues = Class.new(StandardError)
-
-  TIMING_CONFIGURATION = [
-    [0.1.seconds, 0.05.seconds], # short timings, lock_timeout: 100ms, sleep after LockWaitTimeout: 50ms
-    [0.5.seconds, 0.05.seconds],
-    [1.second, 0.5.seconds],
-    [1.second, 0.5.seconds],
-    [5.seconds, 1.second]
-  ].freeze
-
-  def initialize(projects_collection)
-    @root_namespace = projects_collection.take.root_namespace # rubocop:disable CodeReuse/ActiveRecord
-    @base = Issue.in_projects(projects_collection)
-  end
-
-  def execute
-    return unless Feature.enabled?(:rebalance_issues, root_namespace)
-
-    raise TooManyIssues, "#{issue_count} issues" if issue_count > MAX_ISSUE_COUNT
-
-    start = RelativePositioning::START_POSITION - (gaps / 2) * gap_size
-
-    if Feature.enabled?(:issue_rebalancing_optimization)
-      Issue.transaction do
-        assign_positions(start, indexed_ids)
-          .sort_by(&:first)
-          .each_slice(BATCH_SIZE) do |pairs_with_position|
-          if Feature.enabled?(:issue_rebalancing_with_retry)
-            update_positions_with_retry(pairs_with_position, 'rebalance issue positions in batches ordered by id')
-          else
-            update_positions(pairs_with_position, 'rebalance issue positions in batches ordered by id')
-          end
-        end
-      end
-    else
-      Issue.transaction do
-        indexed_ids.each_slice(BATCH_SIZE) do |pairs|
-          pairs_with_position = assign_positions(start, pairs)
-
-          if Feature.enabled?(:issue_rebalancing_with_retry)
-            update_positions_with_retry(pairs_with_position, 'rebalance issue positions')
-          else
-            update_positions(pairs_with_position, 'rebalance issue positions')
-          end
-        end
-      end
-    end
-  end
-
-  private
-
-  attr_reader :root_namespace, :base
-
-  # rubocop: disable CodeReuse/ActiveRecord
-  def indexed_ids
-    base.reorder(:relative_position, :id).pluck(:id).each_with_index
-  end
-  # rubocop: enable CodeReuse/ActiveRecord
-
-  def assign_positions(start, pairs)
-    pairs.map do |id, index|
-      [id, start + (index * gap_size)]
-    end
-  end
-
-  def update_positions_with_retry(pairs_with_position, query_name)
-    retries = 0
-    batch_size = pairs_with_position.size
-
-    until pairs_with_position.empty?
-      begin
-        update_positions(pairs_with_position.first(batch_size), query_name)
-        pairs_with_position = pairs_with_position.drop(batch_size)
-        retries = 0
-      rescue ActiveRecord::StatementTimeout, ActiveRecord::QueryCanceled => ex
-        raise ex if batch_size < SMALLEST_BATCH_SIZE
-
-        if (retries += 1) == RETRIES_LIMIT
-          # shrink the batch size in half when RETRIES limit is reached and update still fails perhaps because batch size is still too big
-          batch_size = (batch_size / 2).to_i
-          retries = 0
-        end
-
-        retry
-      end
-    end
-  end
-
-  def update_positions(pairs_with_position, query_name)
-    values = pairs_with_position.map do |id, index|
-      "(#{id}, #{index})"
-    end.join(', ')
-
-    Gitlab::Database::WithLockRetries.new(timing_configuration: TIMING_CONFIGURATION, klass: self.class).run do
-      run_update_query(values, query_name)
-    end
-  end
-
-  def run_update_query(values, query_name)
-    Issue.connection.exec_query(<<~SQL, query_name)
-      WITH cte(cte_id, new_pos) AS #{Gitlab::Database::AsWithMaterialized.materialized_if_supported} (
-       SELECT *
-       FROM (VALUES #{values}) as t (id, pos)
-      )
-      UPDATE #{Issue.table_name}
-      SET relative_position = cte.new_pos
-      FROM cte
-      WHERE cte_id = id
-    SQL
-  end
-
-  def issue_count
-    @issue_count ||= base.count
-  end
-
-  def gaps
-    issue_count - 1
-  end
-
-  def gap_size
-    # We could try to split the available range over the number of gaps we need,
-    # but IDEAL_DISTANCE * MAX_ISSUE_COUNT is only 0.1% of the available range,
-    # so we are guaranteed not to exhaust it by using this static value.
-    #
-    # If we raise MAX_ISSUE_COUNT or IDEAL_DISTANCE significantly, this may
-    # change!
-    RelativePositioning::IDEAL_DISTANCE
-  end
-end

app/services/issues/relative_position_rebalancing_service.rb

+# frozen_string_literal: true
+
+module Issues
+  class RelativePositionRebalancingService
+    UPDATE_BATCH_SIZE = 100
+    PREFETCH_ISSUES_BATCH_SIZE = 10_000
+    SMALLEST_BATCH_SIZE = 5
+    RETRIES_LIMIT = 3
+
+    TooManyConcurrentRebalances = Class.new(StandardError)
+
+    def initialize(projects)
+      @projects_collection = (projects.is_a?(Array) ? Project.id_in(projects) : projects).projects_order_id_asc
+      @root_namespace = @projects_collection.take.root_namespace # rubocop:disable CodeReuse/ActiveRecord
+      @caching = ::Gitlab::Issues::Rebalancing::State.new(@root_namespace, @projects_collection)
+    end
+
+    def execute
+      return unless Feature.enabled?(:rebalance_issues, root_namespace)
+
+      # Given can_start_rebalance? and track_new_running_rebalance are not atomic
+      # it can happen that we end up with more than Rebalancing::State::MAX_NUMBER_OF_CONCURRENT_REBALANCES running.
+      # Considering the number of allowed Rebalancing::State::MAX_NUMBER_OF_CONCURRENT_REBALANCES is small we should be ok,
+      # but should be something to consider if we'd want to scale this up.
+      error_message = "#{caching.concurrent_running_rebalances_count} concurrent re-balances currently running"
+      raise TooManyConcurrentRebalances, error_message unless caching.can_start_rebalance?
+
+      block_issue_repositioning! unless root_namespace.issue_repositioning_disabled?
+      caching.track_new_running_rebalance
+      index = caching.get_current_index
+
+      loop do
+        issue_ids = get_issue_ids(index, PREFETCH_ISSUES_BATCH_SIZE)
+        pairs_with_index = assign_indexes(issue_ids, index)
+
+        pairs_with_index.each_slice(UPDATE_BATCH_SIZE) do |pairs_batch|
+          update_positions_with_retry(pairs_batch, 're-balance issue positions in batches ordered by position')
+        end
+
+        index = caching.get_current_index
+
+        break if index >= caching.issue_count - 1
+      end
+
+      caching.cleanup_cache
+      unblock_issue_repositioning!
+    end
+
+    private
+
+    attr_reader :root_namespace, :projects_collection, :caching
+
+    def block_issue_repositioning!
+      Feature.enable(:block_issue_repositioning, root_namespace)
+    end
+
+    def unblock_issue_repositioning!
+      Feature.disable(:block_issue_repositioning, root_namespace)
+    end
+
+    def get_issue_ids(index, limit)
+      issue_ids = caching.get_cached_issue_ids(index, limit)
+
+      # if we have a list of cached issues and no current project id cached,
+      # then we successfully cached issues for all projects
+      return issue_ids if issue_ids.any? && caching.get_current_project_id.blank?
+
+      # if we got no issue ids at the start of re-balancing then we did not cache any issue ids yet
+      preload_issue_ids
+
+      caching.get_cached_issue_ids(index, limit)
+    end
+
+    # rubocop: disable CodeReuse/ActiveRecord
+    def preload_issue_ids
+      index = 0
+      cached_project_id = caching.get_current_project_id
+
+      collection = projects_collection
+      collection = projects_collection.where(Project.arel_table[:id].gteq(cached_project_id.to_i)) if cached_project_id.present?
+
+      collection.each do |project|
+        caching.cache_current_project_id(project.id)
+        index += 1
+        scope = Issue.in_projects(project).reorder(custom_reorder).select(:id, :relative_position)
+
+        with_retry(PREFETCH_ISSUES_BATCH_SIZE, 100) do |batch_size|
+          Gitlab::Pagination::Keyset::Iterator.new(scope: scope).each_batch(of: batch_size) do |batch|
+            caching.cache_issue_ids(batch)
+          end
+        end
+      end
+
+      caching.remove_current_project_id_cache
+    end
+    # rubocop: enable CodeReuse/ActiveRecord
+
+    def assign_indexes(ids, start_index)
+      ids.each_with_index.map do |id, idx|
+        [id, start_index + idx]
+      end
+    end
+
+    # The method runs in a loop where we try for RETRIES_LIMIT=3 times, to run the update statement on
+    # a number of records(batch size). Method gets an array of (id, value) pairs as argument that is used
+    # to build the update query matching by id and updating relative_position = value. If we get a statement
+    # timeout, we split the batch size in half and try(for 3 times again) to batch update on a smaller number of records.
+    # On success, because we know the batch size and we always pick from the beginning of the array param,
+    # we can remove first batch_size number of items from array and continue with the successful batch_size for next batches.
+    # On failures we continue to split batch size to a SMALLEST_BATCH_SIZE limit, which is now set at 5.
+    #
+    # e.g.
+    # 0. items | previous batch size|new batch size | comment
+    # 1. 100   | 100                | 100           | 3 failures -> split the batch size in half
+    # 2. 100   | 100                | 50            | 3 failures -> split the batch size in half again
+    # 3. 100   | 50                 | 25            | 3 succeed -> so we drop 25 items 3 times, 4th fails -> split the batch size in half again
+    # 5. 25    | 25                 | 12            | 3 failures -> split the batch size in half
+    # 6. 25    | 12                 | 6             | 3 failures -> we exit because smallest batch size is 5 and we'll be at 3 if we split again
+
+    def update_positions_with_retry(pairs_with_index, query_name)
+      retry_batch_size = pairs_with_index.size
+
+      until pairs_with_index.empty?
+        with_retry(retry_batch_size, SMALLEST_BATCH_SIZE) do |batch_size|
+          retry_batch_size = batch_size
+          update_positions(pairs_with_index.first(batch_size), query_name)
+          # pairs_with_index[batch_size - 1] - can be nil for last batch
+          # if last batch is smaller than batch_size, so we just get the last pair.
+          last_pair_in_batch = pairs_with_index[batch_size - 1] || pairs_with_index.last
+          caching.cache_current_index(last_pair_in_batch.last + 1)
+          pairs_with_index = pairs_with_index.drop(batch_size)
+        end
+      end
+    end
+
+    def update_positions(pairs_with_position, query_name)
+      values = pairs_with_position.map do |id, index|
+        "(#{id}, #{start_position + (index * gap_size)})"
+      end.join(', ')
+
+      run_update_query(values, query_name)
+    end
+
+    def run_update_query(values, query_name)
+      Issue.connection.exec_query(<<~SQL, query_name)
+        WITH cte(cte_id, new_pos) AS #{Gitlab::Database::AsWithMaterialized.materialized_if_supported} (
+         SELECT *
+         FROM (VALUES #{values}) as t (id, pos)
+        )
+        UPDATE #{Issue.table_name}
+        SET relative_position = cte.new_pos
+        FROM cte
+        WHERE cte_id = id
+      SQL
+    end
+
+    def gaps
+      caching.issue_count - 1
+    end
+
+    def gap_size
+      RelativePositioning::MAX_GAP
+    end
+
+    def start_position
+      @start_position ||= (RelativePositioning::START_POSITION - (gaps / 2) * gap_size).to_i
+    end
+
+    def custom_reorder
+      ::Gitlab::Pagination::Keyset::Order.build([Issue.column_order_relative_position, Issue.column_order_id_asc])
+    end
+
+    def with_retry(initial_batch_size, exit_batch_size)
+      retries = 0
+      batch_size = initial_batch_size
+
+      begin
+        yield batch_size
+        retries = 0
+      rescue ActiveRecord::StatementTimeout, ActiveRecord::QueryCanceled => ex
+        raise ex if batch_size < exit_batch_size
+
+        if (retries += 1) == RETRIES_LIMIT
+          # shrink the batch size in half when RETRIES limit is reached and update still fails perhaps because batch size is still too big
+          batch_size = (batch_size / 2).to_i
+          retries = 0
+        end
+
+        retry
+      end
+    end
+  end
+end

app/workers/issue_rebalancing_worker.rb

@@ -32,12 +32,8 @@ class IssueRebalancingWorker
       return
     end
 
-    # Temporary disable rebalancing for performance reasons
-    # For more information check https://gitlab.com/gitlab-com/gl-infra/production/-/issues/4321
-    return if projects_to_rebalance.take&.root_namespace&.issue_repositioning_disabled? # rubocop:disable CodeReuse/ActiveRecord
-
-    IssueRebalancingService.new(projects_to_rebalance).execute
-  rescue IssueRebalancingService::TooManyIssues => e
+    Issues::RelativePositionRebalancingService.new(projects_to_rebalance).execute
+  rescue Issues::RelativePositionRebalancingService::TooManyConcurrentRebalances => e
     Gitlab::ErrorTracking.log_exception(e, root_namespace_id: root_namespace_id, project_id: project_id)
   end
 

config/feature_flags/development/issue_rebalancing_optimization.yml

----
-name: issue_rebalancing_optimization
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/53384
-rollout_issue_url:
-milestone: '13.9'
-type: development
-group: group::project management
-default_enabled: false

config/feature_flags/development/issue_rebalancing_with_retry.yml

----
-name: issue_rebalancing_with_retry
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/59744
-rollout_issue_url:
-milestone: '13.11'
-type: development
-group: group::project management
-default_enabled: false

doc/administration/troubleshooting/gitlab_rails_cheat_sheet.md

@@ -418,7 +418,7 @@ p.create_wiki  ### creates the wiki project on the filesystem
 ```ruby
 p = Project.find_by_full_path('PROJECT PATH')
 
-IssueRebalancingService.new(p.issues.take).execute
+Issues::RelativePositionRebalancingService.new(p.root_namespace.all_projects).execute
 ```
 
 ## Imports / Exports

lib/gitlab/email/handler/create_issue_handler.rb

@@ -55,7 +55,7 @@ module Gitlab
         private
 
         def create_issue
-          Issues::CreateService.new(
+          ::Issues::CreateService.new(
             project: project,
             current_user: author,
             params: {

lib/gitlab/email/handler/service_desk_handler.rb

@@ -71,7 +71,7 @@ module Gitlab
         end
 
         def create_issue!
-          @issue = Issues::CreateService.new(
+          @issue = ::Issues::CreateService.new(
             project: project,
             current_user: User.support_bot,
             params: {

lib/gitlab/issues/rebalancing/state.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Issues
+    module Rebalancing
+      class State
+        REDIS_EXPIRY_TIME = 10.days
+        MAX_NUMBER_OF_CONCURRENT_REBALANCES = 5
+        NAMESPACE = 1
+        PROJECT = 2
+
+        def initialize(root_namespace, projects)
+          @root_namespace = root_namespace
+          @projects = projects
+          @rebalanced_container_type = @root_namespace.is_a?(Group) ? NAMESPACE : PROJECT
+          @rebalanced_container_id = @rebalanced_container_type == NAMESPACE ? @root_namespace.id : projects.take.id # rubocop:disable CodeReuse/ActiveRecord
+        end
+
+        def track_new_running_rebalance
+          with_redis do |redis|
+            redis.multi do |multi|
+              # we trigger re-balance for namespaces(groups) or specific user project
+              value = "#{rebalanced_container_type}/#{rebalanced_container_id}"
+              multi.sadd(concurrent_running_rebalances_key, value)
+              multi.expire(concurrent_running_rebalances_key, REDIS_EXPIRY_TIME)
+            end
+          end
+        end
+
+        def concurrent_running_rebalances_count
+          with_redis { |redis| redis.scard(concurrent_running_rebalances_key).to_i }
+        end
+
+        def rebalance_in_progress?
+          all_rebalanced_containers = with_redis { |redis| redis.smembers(concurrent_running_rebalances_key) }
+
+          is_running = case rebalanced_container_type
+                       when NAMESPACE
+                         namespace_ids = all_rebalanced_containers.map {|string| string.split("#{NAMESPACE}/").second.to_i }.compact
+                         namespace_ids.include?(root_namespace.id)
+                       when PROJECT
+                         project_ids = all_rebalanced_containers.map {|string| string.split("#{PROJECT}/").second.to_i }.compact
+                         project_ids.include?(projects.take.id) # rubocop:disable CodeReuse/ActiveRecord
+                       else
+                         false
+                       end
+
+          refresh_keys_expiration if is_running
+
+          is_running
+        end
+
+        def can_start_rebalance?
+          rebalance_in_progress? || too_many_rebalances_running?
+        end
+
+        def cache_issue_ids(issue_ids)
+          with_redis do |redis|
+            values = issue_ids.map { |issue| [issue.relative_position, issue.id] }
+
+            redis.multi do |multi|
+              multi.zadd(issue_ids_key, values) unless values.blank?
+              multi.expire(issue_ids_key, REDIS_EXPIRY_TIME)
+            end
+          end
+        end
+
+        def get_cached_issue_ids(index, limit)
+          with_redis do |redis|
+            redis.zrange(issue_ids_key, index, index + limit - 1)
+          end
+        end
+
+        def cache_current_index(index)
+          with_redis { |redis| redis.set(current_index_key, index, ex: REDIS_EXPIRY_TIME) }
+        end
+
+        def get_current_index
+          with_redis { |redis| redis.get(current_index_key).to_i }
+        end
+
+        def cache_current_project_id(project_id)
+          with_redis { |redis| redis.set(current_project_key, project_id, ex: REDIS_EXPIRY_TIME) }
+        end
+
+        def get_current_project_id
+          with_redis { |redis| redis.get(current_project_key) }
+        end
+
+        def issue_count
+          @issue_count ||= with_redis { |redis| redis.zcard(issue_ids_key)}
+        end
+
+        def remove_current_project_id_cache
+          with_redis { |redis| redis.del(current_project_key)}
+        end
+
+        def refresh_keys_expiration
+          with_redis do |redis|
+            redis.multi do |multi|
+              multi.expire(issue_ids_key, REDIS_EXPIRY_TIME)
+              multi.expire(current_index_key, REDIS_EXPIRY_TIME)
+              multi.expire(current_project_key, REDIS_EXPIRY_TIME)
+              multi.expire(concurrent_running_rebalances_key, REDIS_EXPIRY_TIME)
+            end
+          end
+        end
+
+        def cleanup_cache
+          with_redis do |redis|
+            redis.multi do |multi|
+              multi.del(issue_ids_key)
+              multi.del(current_index_key)
+              multi.del(current_project_key)
+              multi.srem(concurrent_running_rebalances_key, "#{rebalanced_container_type}/#{rebalanced_container_id}")
+            end
+          end
+        end
+
+        private
+
+        attr_accessor :root_namespace, :projects, :rebalanced_container_type, :rebalanced_container_id
+
+        def too_many_rebalances_running?
+          concurrent_running_rebalances_count <= MAX_NUMBER_OF_CONCURRENT_REBALANCES
+        end
+
+        def redis_key_prefix
+          "gitlab:issues-position-rebalances"
+        end
+
+        def issue_ids_key
+          "#{redis_key_prefix}:#{root_namespace.id}"
+        end
+
+        def current_index_key
+          "#{issue_ids_key}:current_index"
+        end
+
+        def current_project_key
+          "#{issue_ids_key}:current_project_id"
+        end
+
+        def concurrent_running_rebalances_key
+          "#{redis_key_prefix}:running_rebalances"
+        end
+
+        def with_redis(&blk)
+          Gitlab::Redis::SharedState.with(&blk) # rubocop: disable CodeReuse/ActiveRecord
+        end
+      end
+    end
+  end
+end

lib/gitlab/pagination/keyset/order.rb

@@ -219,7 +219,7 @@ module Gitlab
             column_definition.column_expression.dup.as(column_definition.attribute_name).to_sql
           end
 
-          scope = scope.select(*scope.arel.projections, *additional_projections) if additional_projections
+          scope = scope.reselect(*scope.arel.projections, *additional_projections) unless additional_projections.blank?
           scope
         end
 

lib/gitlab/quick_actions/issue_actions.rb

@@ -267,7 +267,7 @@ module Gitlab
         private
 
         def zoom_link_service
-          Issues::ZoomLinkService.new(project: quick_action_target.project, current_user: current_user, params: { issue: quick_action_target })
+          ::Issues::ZoomLinkService.new(project: quick_action_target.project, current_user: current_user, params: { issue: quick_action_target })
         end
       end
     end

lib/gitlab/slash_commands/issue_close.rb

@@ -29,7 +29,7 @@ module Gitlab
       private
 
       def close_issue(issue:)
-        Issues::CloseService.new(project: project, current_user: current_user).execute(issue)
+        ::Issues::CloseService.new(project: project, current_user: current_user).execute(issue)
       end
 
       def presenter(issue)

lib/gitlab/slash_commands/issue_move.rb

@@ -29,11 +29,11 @@ module Gitlab
           return Gitlab::SlashCommands::Presenters::Access.new.not_found
         end
 
-        new_issue = Issues::MoveService.new(project: project, current_user: current_user)
+        new_issue = ::Issues::MoveService.new(project: project, current_user: current_user)
                       .execute(old_issue, target_project)
 
         presenter(new_issue).present(old_issue)
-      rescue Issues::MoveService::MoveError => e
+      rescue ::Issues::MoveService::MoveError => e
         presenter(old_issue).display_move_error(e.message)
       end
 

lib/gitlab/slash_commands/issue_new.rb

@@ -33,7 +33,7 @@ module Gitlab
       private
 
       def create_issue(title:, description:)
-        Issues::CreateService.new(project: project, current_user: current_user, params: { title: title, description: description }, spam_params: nil).execute
+        ::Issues::CreateService.new(project: project, current_user: current_user, params: { title: title, description: description }, spam_params: nil).execute
       end
 
       def presenter(issue)

lib/gitlab/usage_data.rb

@@ -918,7 +918,7 @@ module Gitlab
           jira: count(::JiraImportState.where(time_period)), # rubocop: disable CodeReuse/ActiveRecord
           fogbugz: projects_imported_count('fogbugz', time_period),
           phabricator: projects_imported_count('phabricator', time_period),
-          csv: count(Issues::CsvImport.where(time_period)) # rubocop: disable CodeReuse/ActiveRecord
+          csv: count(::Issues::CsvImport.where(time_period)) # rubocop: disable CodeReuse/ActiveRecord
         }
       end
 
@@ -934,7 +934,7 @@ module Gitlab
         project_imports = distinct_count(::Project.where(time_period).where.not(import_type: nil), :creator_id)
         bulk_imports = distinct_count(::BulkImport.where(time_period), :user_id)
         jira_issue_imports = distinct_count(::JiraImportState.where(time_period), :user_id)
-        csv_issue_imports = distinct_count(Issues::CsvImport.where(time_period), :user_id)
+        csv_issue_imports = distinct_count(::Issues::CsvImport.where(time_period), :user_id)
         group_imports = distinct_count(::GroupImportState.where(time_period), :user_id)
 
         add(project_imports, bulk_imports, jira_issue_imports, csv_issue_imports, group_imports)

spec/lib/gitlab/issues/rebalancing/state_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Issues::Rebalancing::State, :clean_gitlab_redis_shared_state do
+  shared_examples 'issues rebalance caching' do
+    describe '#track_new_running_rebalance' do
+      it 'caches a project id to track caching in progress' do
+        expect { rebalance_caching.track_new_running_rebalance }.to change { rebalance_caching.concurrent_running_rebalances_count }.from(0).to(1)
+      end
+    end
+
+    describe '#set and get current_index' do
+      it 'returns zero as current index when index not cached' do
+        expect(rebalance_caching.get_current_index).to eq(0)
+      end
+
+      it 'returns cached current index' do
+        expect { rebalance_caching.cache_current_index(123) }.to change { rebalance_caching.get_current_index }.from(0).to(123)
+      end
+    end
+
+    describe '#set and get current_project' do
+      it 'returns nil if there is no project_id cached' do
+        expect(rebalance_caching.get_current_project_id).to be_nil
+      end
+
+      it 'returns cached current project_id' do
+        expect { rebalance_caching.cache_current_project_id(456) }.to change { rebalance_caching.get_current_project_id }.from(nil).to('456')
+      end
+    end
+
+    describe "#rebalance_in_progress?" do
+      it 'return zero if no re-balances are running' do
+        expect(rebalance_caching.concurrent_running_rebalances_count).to eq(0)
+      end
+
+      it 'return false if no re-balances are running' do
+        expect(rebalance_caching.rebalance_in_progress?).to be false
+      end
+
+      it 'return true a re-balance for given project/namespace is running' do
+        rebalance_caching.track_new_running_rebalance
+
+        expect(rebalance_caching.rebalance_in_progress?).to be true
+      end
+    end
+
+    context 'caching issue ids' do
+      context 'with no issue ids cached' do
+        it 'returns zero when there are no cached issue ids' do
+          expect(rebalance_caching.issue_count).to eq(0)
+        end
+
+        it 'returns empty array when there are no cached issue ids' do
+          expect(rebalance_caching.get_cached_issue_ids(0, 100)).to eq([])
+        end
+      end
+
+      context 'with cached issue ids' do
+        before do
+          generate_and_cache_issues_ids(count: 3)
+        end
+
+        it 'returns count of cached issue ids' do
+          expect(rebalance_caching.issue_count).to eq(3)
+        end
+
+        it 'returns array of issue ids' do
+          expect(rebalance_caching.get_cached_issue_ids(0, 100)).to eq(%w(1 2 3))
+        end
+
+        it 'limits returned values' do
+          expect(rebalance_caching.get_cached_issue_ids(0, 2)).to eq(%w(1 2))
+        end
+
+        context 'when caching duplicate issue_ids' do
+          before do
+            generate_and_cache_issues_ids(count: 3, position_offset: 3, position_direction: -1)
+          end
+
+          it 'does not cache duplicate issues' do
+            expect(rebalance_caching.issue_count).to eq(3)
+          end
+
+          it 'returns cached issues with latest scores' do
+            expect(rebalance_caching.get_cached_issue_ids(0, 100)).to eq(%w(3 2 1))
+          end
+        end
+      end
+    end
+
+    context 'when setting expiration' do
+      context 'when tracking new rebalance' do
+        it 'returns as expired for non existent key' do
+          ::Gitlab::Redis::SharedState.with do |redis|
+            expect(redis.ttl(rebalance_caching.send(:concurrent_running_rebalances_key))).to be < 0
+          end
+        end
+
+        it 'has expiration set' do
+          rebalance_caching.track_new_running_rebalance
+
+          ::Gitlab::Redis::SharedState.with do |redis|
+            expect(redis.ttl(rebalance_caching.send(:concurrent_running_rebalances_key))).to be_between(0, described_class::REDIS_EXPIRY_TIME.ago.to_i)
+          end
+        end
+      end
+
+      context 'when setting current index' do
+        it 'returns as expiring for non existent key' do
+          ::Gitlab::Redis::SharedState.with do |redis|
+            expect(redis.ttl(rebalance_caching.send(:current_index_key))).to be < 0
+          end
+        end
+
+        it 'has expiration set' do
+          rebalance_caching.cache_current_index(123)
+
+          ::Gitlab::Redis::SharedState.with do |redis|
+            expect(redis.ttl(rebalance_caching.send(:current_index_key))).to be_between(0, described_class::REDIS_EXPIRY_TIME.ago.to_i)
+          end
+        end
+      end
+
+      context 'when setting current project id' do
+        it 'returns as expired for non existent key' do
+          ::Gitlab::Redis::SharedState.with do |redis|
+            expect(redis.ttl(rebalance_caching.send(:current_project_key))).to be < 0
+          end
+        end
+
+        it 'has expiration set' do
+          rebalance_caching.cache_current_project_id(456)
+
+          ::Gitlab::Redis::SharedState.with do |redis|
+            expect(redis.ttl(rebalance_caching.send(:current_project_key))).to be_between(0, described_class::REDIS_EXPIRY_TIME.ago.to_i)
+          end
+        end
+      end
+
+      context 'when setting cached issue ids' do
+        it 'returns as expired for non existent key' do
+          ::Gitlab::Redis::SharedState.with do |redis|
+            expect(redis.ttl(rebalance_caching.send(:issue_ids_key))).to be < 0
+          end
+        end
+
+        it 'has expiration set' do
+          generate_and_cache_issues_ids(count: 3)
+
+          ::Gitlab::Redis::SharedState.with do |redis|
+            expect(redis.ttl(rebalance_caching.send(:issue_ids_key))).to be_between(0, described_class::REDIS_EXPIRY_TIME.ago.to_i)
+          end
+        end
+      end
+    end
+
+    context 'cleanup cache' do
+      before do
+        generate_and_cache_issues_ids(count: 3)
+        rebalance_caching.cache_current_index(123)
+        rebalance_caching.cache_current_project_id(456)
+        rebalance_caching.track_new_running_rebalance
+      end
+
+      it 'removes cache keys' do
+        expect(check_existing_keys).to eq(4)
+
+        rebalance_caching.cleanup_cache
+
+        expect(check_existing_keys).to eq(0)
+      end
+    end
+  end
+
+  context 'rebalancing issues in namespace' do
+    let_it_be(:group) { create(:group, :private) }
+    let_it_be(:project) { create(:project, namespace: group) }
+
+    subject(:rebalance_caching) { described_class.new(group, group.projects) }
+
+    it { expect(rebalance_caching.send(:rebalanced_container_type)).to eq(described_class::NAMESPACE) }
+
+    it_behaves_like 'issues rebalance caching'
+  end
+
+  context 'rebalancing issues in a project' do
+    let_it_be(:project) { create(:project) }
+
+    subject(:rebalance_caching) { described_class.new(project.namespace, Project.where(id: project)) }
+
+    it { expect(rebalance_caching.send(:rebalanced_container_type)).to eq(described_class::PROJECT) }
+
+    it_behaves_like 'issues rebalance caching'
+  end
+
+  # count - how many issue ids to generate, issue ids will start at 1
+  # position_offset - if you'd want to offset generated relative_position for the issue ids,
+  # relative_position is generated as = issue id * 10 + position_offset
+  # position_direction - (1) for positive relative_positions, (-1) for negative relative_positions
+  def generate_and_cache_issues_ids(count:, position_offset: 0, position_direction: 1)
+    issues = []
+
+    count.times do |idx|
+      id = idx + 1
+      issues << double(relative_position: position_direction * (id * 10 + position_offset), id: id)
+    end
+
+    rebalance_caching.cache_issue_ids(issues)
+  end
+
+  def check_existing_keys
+    index = 0
+
+    index += 1 if rebalance_caching.get_current_index > 0
+    index += 1 if rebalance_caching.get_current_project_id.present?
+    index += 1 if rebalance_caching.get_cached_issue_ids(0, 100).present?
+    index += 1 if rebalance_caching.rebalance_in_progress?
+
+    index
+  end
+end

spec/lib/gitlab/pagination/keyset/order_spec.rb

@@ -538,6 +538,47 @@ RSpec.describe Gitlab::Pagination::Keyset::Order do
         end
 
         it_behaves_like 'cursor attribute examples'
+
+        context 'with projections' do
+          context 'when additional_projections is empty' do
+            let(:scope) { Project.select(:id, :namespace_id) }
+
+            subject(:sql) { order.apply_cursor_conditions(scope, { id: '100' }).to_sql }
+
+            it 'has correct projections' do
+              is_expected.to include('SELECT "projects"."id", "projects"."namespace_id" FROM "projects"')
+            end
+          end
+
+          context 'when there are additional_projections' do
+            let(:order) do
+              order = Gitlab::Pagination::Keyset::Order.build([
+                Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
+                  attribute_name: 'created_at_field',
+                  column_expression: Project.arel_table[:created_at],
+                  order_expression: Project.arel_table[:created_at].desc,
+                  order_direction: :desc,
+                  distinct: false,
+                  add_to_projections: true
+                ),
+                Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
+                  attribute_name: 'id',
+                  order_expression: Project.arel_table[:id].desc
+                )
+              ])
+
+              order
+            end
+
+            let(:scope) { Project.select(:id, :namespace_id).reorder(order) }
+
+            subject(:sql) { order.apply_cursor_conditions(scope).to_sql }
+
+            it 'has correct projections' do
+              is_expected.to include('SELECT "projects"."id", "projects"."namespace_id", "projects"."created_at" AS created_at_field FROM "projects"')
+            end
+          end
+        end
       end
     end
   end

spec/services/issue_rebalancing_service_spec.rb → spec/services/issues/relative_position_rebalancing_service_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-RSpec.describe IssueRebalancingService do
+RSpec.describe Issues::RelativePositionRebalancingService, :clean_gitlab_redis_shared_state do
   let_it_be(:project, reload: true) { create(:project) }
   let_it_be(:user) { project.creator }
   let_it_be(:start) { RelativePositioning::START_POSITION }
@@ -36,10 +36,11 @@ RSpec.describe IssueRebalancingService do
     project.reload.issues.reorder(relative_position: :asc).to_a
   end
 
-  shared_examples 'IssueRebalancingService shared examples' do
-    it 'rebalances a set of issues with clumps at the end and start' do
+  subject(:service) { described_class.new(Project.id_in(project)) }
+
+  context 'execute' do
+    it 're-balances a set of issues with clumps at the end and start' do
       all_issues = start_clump + unclumped + end_clump.reverse
-      service = described_class.new(Project.id_in([project.id]))
 
       expect { service.execute }.not_to change { issues_in_position_order.map(&:id) }
 
@@ -52,11 +53,10 @@ RSpec.describe IssueRebalancingService do
       expect(gaps).to all(be > RelativePositioning::MIN_GAP)
       expect(all_issues.first.relative_position).to be > (RelativePositioning::MIN_POSITION * 0.9999)
       expect(all_issues.last.relative_position).to be < (RelativePositioning::MAX_POSITION * 0.9999)
+      expect(project.root_namespace.issue_repositioning_disabled?).to be false
     end
 
     it 'is idempotent' do
-      service = described_class.new(Project.id_in(project))
-
       expect do
         service.execute
         service.execute
@@ -70,9 +70,9 @@ RSpec.describe IssueRebalancingService do
       issue.project.group
       old_pos = issue.relative_position
 
-      service = described_class.new(Project.id_in(project))
-
-      expect { service.execute }.not_to exceed_query_limit(0)
+      # fetching root namespace in the initializer triggers 2 queries:
+      # for fetching a random project from collection and fetching the root namespace.
+      expect { service.execute }.not_to exceed_query_limit(2)
       expect(old_pos).to eq(issue.reload.relative_position)
     end
 
@@ -80,8 +80,6 @@ RSpec.describe IssueRebalancingService do
       issue = create(:issue, project: project, author: user, relative_position: max_pos)
       stub_feature_flags(rebalance_issues: project.root_namespace)
 
-      service = described_class.new(Project.id_in(project))
-
       expect { service.execute }.to change { issue.reload.relative_position }
     end
 
@@ -90,22 +88,34 @@ RSpec.describe IssueRebalancingService do
       project.update!(group: create(:group))
       stub_feature_flags(rebalance_issues: issue.project.group)
 
-      service = described_class.new(Project.id_in(project))
-
       expect { service.execute }.to change { issue.reload.relative_position }
     end
 
-    it 'aborts if there are too many issues' do
-      base = double(count: 10_001)
+    it 'aborts if there are too many rebalances running' do
+      caching = service.send(:caching)
+      allow(caching).to receive(:rebalance_in_progress?).and_return(false)
+      allow(caching).to receive(:concurrent_running_rebalances_count).and_return(10)
+      allow(service).to receive(:caching).and_return(caching)
 
-      allow(Issue).to receive(:in_projects).and_return(base)
+      expect { service.execute }.to raise_error(Issues::RelativePositionRebalancingService::TooManyConcurrentRebalances)
+      expect(project.root_namespace.issue_repositioning_disabled?).to be false
+    end
 
-      expect { described_class.new(Project.id_in(project)).execute }.to raise_error(described_class::TooManyIssues)
+    it 'resumes a started rebalance even if there are already too many rebalances running' do
+      Gitlab::Redis::SharedState.with do |redis|
+        redis.sadd("gitlab:issues-position-rebalances:running_rebalances", "#{::Gitlab::Issues::Rebalancing::State::PROJECT}/#{project.id}")
+        redis.sadd("gitlab:issues-position-rebalances:running_rebalances", "1/100")
       end
+
+      caching = service.send(:caching)
+      allow(caching).to receive(:concurrent_running_rebalances_count).and_return(10)
+      allow(service).to receive(:caching).and_return(caching)
+
+      expect { service.execute }.not_to raise_error(Issues::RelativePositionRebalancingService::TooManyConcurrentRebalances)
     end
 
-  shared_examples 'rebalancing is retried on statement timeout exceptions' do
-    subject { described_class.new(Project.id_in(project)) }
+    context 're-balancing is retried on statement timeout exceptions' do
+      subject { service }
 
       it 'retries update statement' do
         call_count = 0
@@ -137,37 +147,20 @@ RSpec.describe IssueRebalancingService do
       end
     end
 
-  context 'when issue_rebalancing_optimization feature flag is on' do
+    context 'when resuming a stopped rebalance' do
       before do
-      stub_feature_flags(issue_rebalancing_optimization: true)
+        service.send(:preload_issue_ids)
+        expect(service.send(:caching).get_cached_issue_ids(0, 300)).not_to be_empty
+        # simulate we already rebalanced half the issues
+        index = clump_size * 3 / 2 + 1
+        service.send(:caching).cache_current_index(index)
       end
 
-    it_behaves_like 'IssueRebalancingService shared examples'
-
-    context 'when issue_rebalancing_with_retry feature flag is on' do
-      before do
-        stub_feature_flags(issue_rebalancing_with_retry: true)
-      end
+      it 'rebalances the other half of issues' do
+        expect(subject).to receive(:update_positions_with_retry).exactly(5).and_call_original
 
-      it_behaves_like 'IssueRebalancingService shared examples'
-      it_behaves_like 'rebalancing is retried on statement timeout exceptions'
-    end
-  end
-
-  context 'when issue_rebalancing_optimization feature flag is off' do
-    before do
-      stub_feature_flags(issue_rebalancing_optimization: false)
-    end
-
-    it_behaves_like 'IssueRebalancingService shared examples'
-
-    context 'when issue_rebalancing_with_retry feature flag is on' do
-      before do
-        stub_feature_flags(issue_rebalancing_with_retry: true)
+        subject.execute
       end
-
-      it_behaves_like 'IssueRebalancingService shared examples'
-      it_behaves_like 'rebalancing is retried on statement timeout exceptions'
     end
   end
 end

spec/workers/issue_rebalancing_worker_spec.rb

@@ -8,41 +8,29 @@ RSpec.describe IssueRebalancingWorker do
     let_it_be(:project) { create(:project, group: group) }
     let_it_be(:issue) { create(:issue, project: project) }
 
-    context 'when block_issue_repositioning is enabled' do
-      before do
-        stub_feature_flags(block_issue_repositioning: group)
-      end
-
-      it 'does not run an instance of IssueRebalancingService' do
-        expect(IssueRebalancingService).not_to receive(:new)
-
-        described_class.new.perform(nil, issue.project_id)
-      end
-    end
-
     shared_examples 'running the worker' do
-      it 'runs an instance of IssueRebalancingService' do
+      it 'runs an instance of Issues::RelativePositionRebalancingService' do
         service = double(execute: nil)
         service_param = arguments.second.present? ? kind_of(Project.id_in([project]).class) : kind_of(group&.all_projects.class)
 
-        expect(IssueRebalancingService).to receive(:new).with(service_param).and_return(service)
+        expect(Issues::RelativePositionRebalancingService).to receive(:new).with(service_param).and_return(service)
 
         described_class.new.perform(*arguments)
       end
 
-      it 'anticipates there being too many issues' do
+      it 'anticipates there being too many concurent rebalances' do
         service = double
         service_param = arguments.second.present? ? kind_of(Project.id_in([project]).class) : kind_of(group&.all_projects.class)
 
-        allow(service).to receive(:execute).and_raise(IssueRebalancingService::TooManyIssues)
-        expect(IssueRebalancingService).to receive(:new).with(service_param).and_return(service)
-        expect(Gitlab::ErrorTracking).to receive(:log_exception).with(IssueRebalancingService::TooManyIssues, include(project_id: arguments.second, root_namespace_id: arguments.third))
+        allow(service).to receive(:execute).and_raise(Issues::RelativePositionRebalancingService::TooManyConcurrentRebalances)
+        expect(Issues::RelativePositionRebalancingService).to receive(:new).with(service_param).and_return(service)
+        expect(Gitlab::ErrorTracking).to receive(:log_exception).with(Issues::RelativePositionRebalancingService::TooManyConcurrentRebalances, include(project_id: arguments.second, root_namespace_id: arguments.third))
 
         described_class.new.perform(*arguments)
       end
 
       it 'takes no action if the value is nil' do
-        expect(IssueRebalancingService).not_to receive(:new)
+        expect(Issues::RelativePositionRebalancingService).not_to receive(:new)
         expect(Gitlab::ErrorTracking).not_to receive(:log_exception)
 
         described_class.new.perform # all arguments are nil
@@ -52,7 +40,7 @@ RSpec.describe IssueRebalancingWorker do
     shared_examples 'safely handles non-existent ids' do
       it 'anticipates the inability to find the issue' do
         expect(Gitlab::ErrorTracking).to receive(:log_exception).with(ArgumentError, include(project_id: arguments.second, root_namespace_id: arguments.third))
-        expect(IssueRebalancingService).not_to receive(:new)
+        expect(Issues::RelativePositionRebalancingService).not_to receive(:new)
 
         described_class.new.perform(*arguments)
       end