Remove gitlab_structure.sql and related tasks

Delete the `db/gitlab_structure.sql` file, which was previously
introduced to support partitioned foreign keys in pre-PG12 databases.

Also remove the corresponding code and rake tasks that maintain this
file.

db/gitlab_structure.sql

--- this file tracks custom GitLab data, such as foreign keys referencing partitioned tables
--- more details can be found in the issue: https://gitlab.com/gitlab-org/gitlab/-/issues/201872
-

lib/gitlab/database/custom_structure.rb

-# frozen_string_literal: true
-
-module Gitlab
-  module Database
-    class CustomStructure
-      CUSTOM_DUMP_FILE = 'db/gitlab_structure.sql'
-
-      def dump
-        File.open(self.class.custom_dump_filepath, 'wb') do |io|
-          io << "-- this file tracks custom GitLab data, such as foreign keys referencing partitioned tables\n"
-          io << "-- more details can be found in the issue: https://gitlab.com/gitlab-org/gitlab/-/issues/201872\n\n"
-
-          dump_partitioned_foreign_keys(io) if partitioned_foreign_keys_exist?
-        end
-      end
-
-      def self.custom_dump_filepath
-        Rails.root.join(CUSTOM_DUMP_FILE)
-      end
-
-      private
-
-      def dump_partitioned_foreign_keys(io)
-        io << "COPY partitioned_foreign_keys (#{partitioned_fk_columns.join(", ")}) FROM STDIN;\n"
-
-        PartitioningMigrationHelpers::PartitionedForeignKey.find_each do |fk|
-          io << fk.attributes.values_at(*partitioned_fk_columns).join("\t") << "\n"
-        end
-        io << "\\.\n"
-      end
-
-      def partitioned_foreign_keys_exist?
-        return false unless PartitioningMigrationHelpers::PartitionedForeignKey.table_exists?
-
-        PartitioningMigrationHelpers::PartitionedForeignKey.exists?
-      end
-
-      def partitioned_fk_columns
-        @partitioned_fk_columns ||= PartitioningMigrationHelpers::PartitionedForeignKey.column_names
-      end
-    end
-  end
-end

lib/tasks/gitlab/db.rake

@@ -101,57 +101,16 @@ namespace :gitlab do
       Rake::Task[task_name].reenable
     end
 
-    desc 'This dumps GitLab specific database details - it runs after db:structure:dump'
-    task :dump_custom_structure do |task_name|
-      Gitlab::Database::CustomStructure.new.dump
-
-      # Allow this task to be called multiple times, as happens when running db:migrate:redo
-      Rake::Task[task_name].reenable
-    end
-
-    desc 'This loads GitLab specific database details - runs after db:structure:dump'
-    task :load_custom_structure do
-      configuration = Rails.application.config_for(:database)
-
-      ENV['PGHOST']     = configuration['host']          if configuration['host']
-      ENV['PGPORT']     = configuration['port'].to_s     if configuration['port']
-      ENV['PGPASSWORD'] = configuration['password'].to_s if configuration['password']
-      ENV['PGUSER']     = configuration['username'].to_s if configuration['username']
-
-      command = 'psql'
-      dump_filepath = Gitlab::Database::CustomStructure.custom_dump_filepath.to_path
-      args = ['-v', 'ON_ERROR_STOP=1', '-q', '-X', '-f', dump_filepath, configuration['database']]
-
-      unless Kernel.system(command, *args)
-        raise "failed to execute:\n#{command} #{args.join(' ')}\n\n" \
-          "Please ensure `#{command}` is installed in your PATH and has proper permissions.\n\n"
-      end
-    end
-
     # Inform Rake that custom tasks should be run every time rake db:structure:dump is run
     #
     # Rails 6.1 deprecates db:structure:dump in favor of db:schema:dump
     Rake::Task['db:structure:dump'].enhance do
       Rake::Task['gitlab:db:clean_structure_sql'].invoke
-      Rake::Task['gitlab:db:dump_custom_structure'].invoke
     end
 
     # Inform Rake that custom tasks should be run every time rake db:schema:dump is run
     Rake::Task['db:schema:dump'].enhance do
       Rake::Task['gitlab:db:clean_structure_sql'].invoke
-      Rake::Task['gitlab:db:dump_custom_structure'].invoke
-    end
-
-    # Inform Rake that custom tasks should be run every time rake db:structure:load is run
-    #
-    # Rails 6.1 deprecates db:structure:load in favor of db:schema:load
-    Rake::Task['db:structure:load'].enhance do
-      Rake::Task['gitlab:db:load_custom_structure'].invoke
-    end
-
-    # Inform Rake that custom tasks should be run every time rake db:schema:load is run
-    Rake::Task['db:schema:load'].enhance do
-      Rake::Task['gitlab:db:load_custom_structure'].invoke
     end
 
     desc 'Create missing dynamic database partitions'

spec/lib/gitlab/database/custom_structure_spec.rb

-# frozen_string_literal: true
-
-require 'spec_helper'
-
-RSpec.describe Gitlab::Database::CustomStructure do
-  let_it_be(:structure) { described_class.new }
-  let_it_be(:filepath) { Rails.root.join(described_class::CUSTOM_DUMP_FILE) }
-  let_it_be(:file_header) do
-    <<~DATA
-      -- this file tracks custom GitLab data, such as foreign keys referencing partitioned tables
-      -- more details can be found in the issue: https://gitlab.com/gitlab-org/gitlab/-/issues/201872
-    DATA
-  end
-
-  let(:io) { StringIO.new }
-
-  before do
-    allow(File).to receive(:open).with(filepath, anything).and_yield(io)
-  end
-
-  context 'when there are no partitioned_foreign_keys' do
-    it 'dumps a valid structure file' do
-      structure.dump
-
-      expect(io.string).to eq("#{file_header}\n")
-    end
-  end
-
-  context 'when there are partitioned_foreign_keys' do
-    let!(:first_fk) do
-      Gitlab::Database::PartitioningMigrationHelpers::PartitionedForeignKey.create(
-        cascade_delete: true, from_table: 'issues', from_column: 'project_id', to_table: 'projects', to_column: 'id')
-    end
-
-    let!(:second_fk) do
-      Gitlab::Database::PartitioningMigrationHelpers::PartitionedForeignKey.create(
-        cascade_delete: false, from_table: 'issues', from_column: 'moved_to_id', to_table: 'issues', to_column: 'id')
-    end
-
-    it 'dumps a file with the command to restore the current keys' do
-      structure.dump
-
-      expect(io.string).to eq(<<~DATA)
-        #{file_header}
-        COPY partitioned_foreign_keys (id, cascade_delete, from_table, from_column, to_table, to_column) FROM STDIN;
-        #{first_fk.id}\ttrue\tissues\tproject_id\tprojects\tid
-        #{second_fk.id}\tfalse\tissues\tmoved_to_id\tissues\tid
-        \\.
-      DATA
-
-      first_fk.destroy
-      io.truncate(0)
-      io.rewind
-
-      structure.dump
-
-      expect(io.string).to eq(<<~DATA)
-        #{file_header}
-        COPY partitioned_foreign_keys (id, cascade_delete, from_table, from_column, to_table, to_column) FROM STDIN;
-        #{second_fk.id}\tfalse\tissues\tmoved_to_id\tissues\tid
-        \\.
-      DATA
-    end
-  end
-end

spec/tasks/gitlab/db_rake_spec.rb

@@ -146,47 +146,6 @@ RSpec.describe 'gitlab:db namespace rake task', :silence_stdout do
     end
   end
 
-  describe 'load_custom_structure' do
-    let_it_be(:db_config) { Rails.application.config_for(:database) }
-    let_it_be(:custom_load_task) { 'gitlab:db:load_custom_structure' }
-    let_it_be(:custom_filepath) { Pathname.new('db/directory') }
-
-    it 'uses the psql command to load the custom structure file' do
-      expect(Gitlab::Database::CustomStructure).to receive(:custom_dump_filepath).and_return(custom_filepath)
-
-      expect(Kernel).to receive(:system)
-        .with('psql', any_args, custom_filepath.to_path, db_config['database']).and_return(true)
-
-      run_rake_task(custom_load_task)
-    end
-
-    it 'raises an error when the call to the psql command fails' do
-      expect(Gitlab::Database::CustomStructure).to receive(:custom_dump_filepath).and_return(custom_filepath)
-
-      expect(Kernel).to receive(:system)
-        .with('psql', any_args, custom_filepath.to_path, db_config['database']).and_return(nil)
-
-      expect { run_rake_task(custom_load_task) }.to raise_error(/failed to execute:\s*psql/)
-    end
-  end
-
-  describe 'dump_custom_structure' do
-    let_it_be(:test_task_name) { 'gitlab:db:_test_multiple_task_executions' }
-    let_it_be(:custom_dump_task) { 'gitlab:db:dump_custom_structure' }
-
-    after do
-      Rake::Task[test_task_name].clear if Rake::Task.task_defined?(test_task_name)
-    end
-
-    it 'can be executed multiple times within another rake task' do
-      expect_multiple_executions_of_task(test_task_name, custom_dump_task) do
-        expect_next_instance_of(Gitlab::Database::CustomStructure) do |custom_structure|
-          expect(custom_structure).to receive(:dump)
-        end
-      end
-    end
-  end
-
   describe 'drop_tables' do
     subject { run_rake_task('gitlab:db:drop_tables') }