BigW Consortium Gitlab

20170530130129_project_foreign_keys_with_cascading_deletes.rb 6.04 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187
# See http://doc.gitlab.com/ce/development/migration_style_guide.html
# for more information on how to write migrations for GitLab.

class ProjectForeignKeysWithCascadingDeletes < ActiveRecord::Migration
  include Gitlab::Database::MigrationHelpers

  DOWNTIME = false

  CONCURRENCY = 4

  disable_ddl_transaction!

  # The tables/columns for which to remove orphans and add foreign keys. Order
  # matters as some tables/columns should be processed before others.
  TABLES = [
    [:boards, :projects, :project_id],
    [:lists, :labels, :label_id],
    [:lists, :boards, :board_id],
    [:services, :projects, :project_id],
    [:forked_project_links, :projects, :forked_to_project_id],
    [:merge_requests, :projects, :target_project_id],
    [:labels, :projects, :project_id],
    [:issues, :projects, :project_id],
    [:events, :projects, :project_id],
    [:milestones, :projects, :project_id],
    [:notes, :projects, :project_id],
    [:snippets, :projects, :project_id],
    [:web_hooks, :projects, :project_id],
    [:protected_branch_merge_access_levels, :protected_branches, :protected_branch_id],
    [:protected_branch_push_access_levels, :protected_branches, :protected_branch_id],
    [:protected_branches, :projects, :project_id],
    [:protected_tags, :projects, :project_id],
    [:deploy_keys_projects, :projects, :project_id],
    [:users_star_projects, :projects, :project_id],
    [:releases, :projects, :project_id],
    [:project_group_links, :projects, :project_id],
    [:pages_domains, :projects, :project_id],
    [:todos, :projects, :project_id],
    [:project_import_data, :projects, :project_id],
    [:project_features, :projects, :project_id],
    [:ci_builds, :projects, :project_id],
    [:ci_pipelines, :projects, :project_id],
    [:ci_runner_projects, :projects, :project_id],
    [:ci_triggers, :projects, :project_id],
    [:environments, :projects, :project_id],
    [:deployments, :projects, :project_id]
  ]

  def up
    # These existing foreign keys don't have an "ON DELETE CASCADE" clause.
    remove_foreign_key_without_error(:boards, :project_id)
    remove_foreign_key_without_error(:lists, :label_id)
    remove_foreign_key_without_error(:lists, :board_id)
    remove_foreign_key_without_error(:protected_branch_merge_access_levels,
                                     :protected_branch_id)

    remove_foreign_key_without_error(:protected_branch_push_access_levels,
                                     :protected_branch_id)

    remove_orphaned_rows
    add_foreign_keys

    # These columns are not indexed yet, meaning a cascading delete would take
    # forever.
    add_concurrent_index(:project_group_links, :project_id)
    add_concurrent_index(:pages_domains, :project_id)
  end

  def down
    TABLES.each do |(source, _, column)|
      remove_foreign_key_without_error(source, column)
    end

    add_concurrent_foreign_key(:boards, :projects, column: :project_id)
    add_concurrent_foreign_key(:lists, :labels, column: :label_id)
    add_concurrent_foreign_key(:lists, :boards, column: :board_id)

    add_concurrent_foreign_key(:protected_branch_merge_access_levels,
                               :protected_branches,
                               column: :protected_branch_id)

    add_concurrent_foreign_key(:protected_branch_push_access_levels,
                               :protected_branches,
                               column: :protected_branch_id)

    remove_index_without_error(:project_group_links, :project_id)
    remove_index_without_error(:pages_domains, :project_id)
  end

  def add_foreign_keys
    TABLES.each do |(source, target, column)|
      add_concurrent_foreign_key(source, target, column: column)
    end
  end

  # Removes orphans from various tables concurrently.
  def remove_orphaned_rows
    Gitlab::Database.with_connection_pool(CONCURRENCY) do |pool|
      queues = queues_for_rows(TABLES)

      threads = queues.map do |queue|
        Thread.new do
          pool.with_connection do |connection|
            Thread.current[:foreign_key_connection] = connection

            # Disables statement timeouts for the current connection. This is
            # necessary as removing of orphaned data might otherwise exceed the
            # statement timeout.
            disable_statement_timeout

            remove_orphans(*queue.pop) until queue.empty?

            steal_from_queues(queues - [queue])
          end
        end
      end

      threads.each(&:join)
    end
  end

  def steal_from_queues(queues)
    loop do
      stolen = false

      queues.each do |queue|
        # Stealing is racy so it's possible a pop might be called on an
        # already-empty queue.
        begin
          remove_orphans(*queue.pop(true))
          stolen = true
        rescue ThreadError
        end
      end

      break unless stolen
    end
  end

  def remove_orphans(source, target, column)
    quoted_source = quote_table_name(source)
    quoted_target = quote_table_name(target)
    quoted_column = quote_column_name(column)

    execute <<-EOF.strip_heredoc
    DELETE FROM #{quoted_source}
    WHERE NOT EXISTS (
      SELECT true
      FROM #{quoted_target}
      WHERE #{quoted_target}.id = #{quoted_source}.#{quoted_column}
    )
    AND #{quoted_source}.#{quoted_column} IS NOT NULL
    EOF
  end

  def remove_foreign_key_without_error(table, column)
    remove_foreign_key(table, column: column)
  rescue ArgumentError
  end

  def remove_index_without_error(table, column)
    remove_concurrent_index(table, column)
  rescue ArgumentError
  end

  def connection
    # Rails memoizes connection objects, but this causes them to be shared
    # amongst threads; we don't want that.
    Thread.current[:foreign_key_connection] || ActiveRecord::Base.connection
  end

  def queues_for_rows(rows)
    queues = Array.new(CONCURRENCY) { Queue.new }
    slice_size = rows.length / CONCURRENCY

    # Divide all the tuples as evenly as possible amongst the queues.
    rows.each_slice(slice_size).each_with_index do |slice, index|
      bucket = index % CONCURRENCY

      slice.each do |row|
        queues[bucket] << row
      end
    end

    queues
  end
end