Merge branch 'ab/reindex-concurrently' into 'master'

Reindexing strategy for PG12

See merge request gitlab-org/gitlab!64695

config/feature_flags/development/database_reindexing_pg12.yml

+---
+name: database_reindexing_pg12
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64695
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/334372
+milestone: '14.1'
+type: development
+group: group::database
+default_enabled: false

lib/gitlab/database/postgres_index.rb

@@ -20,16 +20,25 @@ module Gitlab
       # A 'regular' index is a non-unique index,
       # that does not serve an exclusion constraint and
       # is defined on a table that is not partitioned.
-      scope :regular, -> { where(unique: false, partitioned: false, exclusion: false)}
+      #
+      # Deprecated: Switch to scope .reindexing_support
+      scope :regular, -> { where(unique: false, partitioned: false, exclusion: false, expression: false)}
+
+      # Indexes for reindexing with PG12
+      scope :reindexing_support, -> { where(partitioned: false, exclusion: false, expression: false) }
 
       scope :not_match, ->(regex) { where("name !~ ?", regex)}
 
+      scope :match, ->(regex) { where("name ~* ?", regex)}
+
       scope :not_recently_reindexed, -> do
         recent_actions = Reindexing::ReindexAction.recent.where('index_identifier = identifier')
 
         where('NOT EXISTS (?)', recent_actions)
       end
 
+      alias_method :reset, :reload
+
       def bloat_size
         strong_memoize(:bloat_size) { bloat_estimate&.bloat_size || 0 }
       end

lib/gitlab/database/reindexing.rb

@@ -14,11 +14,16 @@ module Gitlab
       end
 
       def self.candidate_indexes
-        Gitlab::Database::PostgresIndex
-          .regular
-          .where('NOT expression')
+        indexes = Gitlab::Database::PostgresIndex
           .not_match("^#{ConcurrentReindex::TEMPORARY_INDEX_PREFIX}")
           .not_match("^#{ConcurrentReindex::REPLACED_INDEX_PREFIX}")
+          .not_match("#{ReindexConcurrently::TEMPORARY_INDEX_PATTERN}$")
+
+        if Feature.enabled?(:database_reindexing_pg12, type: :development)
+          indexes.reindexing_support
+        else
+          indexes.regular
+        end
       end
     end
   end

lib/gitlab/database/reindexing/coordinator.rb

@@ -41,7 +41,13 @@ module Gitlab
         end
 
         def perform_for(index, action)
-          ConcurrentReindex.new(index).perform
+          strategy = if Feature.enabled?(:database_reindexing_pg12, type: :development)
+                       ReindexConcurrently
+                     else
+                       ConcurrentReindex
+                     end
+
+          strategy.new(index).perform
         rescue StandardError
           action.state = :failed
 

lib/gitlab/database/reindexing/reindex_concurrently.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module Reindexing
+      # This is a >= PG12 reindexing strategy based on `REINDEX CONCURRENTLY`
+      class ReindexConcurrently
+        ReindexError = Class.new(StandardError)
+
+        TEMPORARY_INDEX_PATTERN = '\_ccnew[0-9]*'
+        STATEMENT_TIMEOUT = 9.hours
+        PG_MAX_INDEX_NAME_LENGTH = 63
+
+        # When dropping an index, we acquire a SHARE UPDATE EXCLUSIVE lock,
+        # which only conflicts with DDL and vacuum. We therefore execute this with a rather
+        # high lock timeout and a long pause in between retries. This is an alternative to
+        # setting a high statement timeout, which would lead to a long running query with effects
+        # on e.g. vacuum.
+        REMOVE_INDEX_RETRY_CONFIG = [[1.minute, 9.minutes]] * 30
+
+        attr_reader :index, :logger
+
+        def initialize(index, logger: Gitlab::AppLogger)
+          @index = index
+          @logger = logger
+        end
+
+        def perform
+          raise ReindexError, 'indexes serving an exclusion constraint are currently not supported' if index.exclusion?
+          raise ReindexError, 'index is a left-over temporary index from a previous reindexing run' if index.name =~ /#{TEMPORARY_INDEX_PATTERN}/
+
+          # Expression indexes require additional statistics in `pg_statistic`:
+          # select * from pg_statistic where starelid = (select oid from pg_class where relname = 'some_index');
+          #
+          # In PG12, this has been fixed in https://gitlab.com/postgres/postgres/-/commit/b17ff07aa3eb142d2cde2ea00e4a4e8f63686f96.
+          # Discussion happened in https://www.postgresql.org/message-id/flat/CAFcNs%2BqpFPmiHd1oTXvcPdvAHicJDA9qBUSujgAhUMJyUMb%2BSA%40mail.gmail.com
+          # following a GitLab.com incident that surfaced this (https://gitlab.com/gitlab-com/gl-infra/production/-/issues/2885).
+          #
+          # While this has been backpatched, we continue to disable expression indexes until further review.
+          raise ReindexError, 'expression indexes are currently not supported' if index.expression?
+
+          begin
+            with_logging do
+              set_statement_timeout do
+                execute("REINDEX INDEX CONCURRENTLY #{quote_table_name(index.schema)}.#{quote_table_name(index.name)}")
+              end
+            end
+          ensure
+            cleanup_dangling_indexes
+          end
+        end
+
+        private
+
+        def with_logging
+          bloat_size = index.bloat_size
+          ondisk_size_before = index.ondisk_size_bytes
+
+          logger.info(
+            message: "Starting reindex of #{index}",
+            index: index.identifier,
+            table: index.tablename,
+            estimated_bloat_bytes: bloat_size,
+            index_size_before_bytes: ondisk_size_before
+          )
+
+          duration = Benchmark.realtime do
+            yield
+          end
+
+          index.reset
+
+          logger.info(
+            message: "Finished reindex of #{index}",
+            index: index.identifier,
+            table: index.tablename,
+            estimated_bloat_bytes: bloat_size,
+            index_size_before_bytes: ondisk_size_before,
+            index_size_after_bytes: index.ondisk_size_bytes,
+            duration_s: duration.round(2)
+          )
+        end
+
+        def cleanup_dangling_indexes
+          Gitlab::Database::PostgresIndex.match("#{TEMPORARY_INDEX_PATTERN}$").each do |lingering_index|
+            # Example lingering index name: some_index_ccnew1
+
+            # Example prefix: 'some_index'
+            prefix = lingering_index.name.gsub(/#{TEMPORARY_INDEX_PATTERN}/, '')
+
+            # Example suffix: '_ccnew1'
+            suffix = lingering_index.name.match(/#{TEMPORARY_INDEX_PATTERN}/)[0]
+
+            # Only remove if the lingering index name could have been chosen
+            # as a result of a REINDEX operation (considering that PostgreSQL
+            # truncates index names to 63 chars and adds a suffix).
+            if index.name[0...PG_MAX_INDEX_NAME_LENGTH - suffix.length] == prefix
+              remove_index(lingering_index)
+            end
+          end
+        end
+
+        def remove_index(index)
+          logger.info("Removing dangling index #{index.identifier}")
+
+          retries = Gitlab::Database::WithLockRetriesOutsideTransaction.new(
+            timing_configuration: REMOVE_INDEX_RETRY_CONFIG,
+            klass: self.class,
+            logger: logger
+          )
+
+          retries.run(raise_on_exhaustion: false) do
+            execute("DROP INDEX CONCURRENTLY IF EXISTS #{quote_table_name(index.schema)}.#{quote_table_name(index.name)}")
+          end
+        end
+
+        def with_lock_retries(&block)
+          arguments = { klass: self.class, logger: logger }
+          Gitlab::Database::WithLockRetries.new(**arguments).run(raise_on_exhaustion: true, &block)
+        end
+
+        def set_statement_timeout
+          execute("SET statement_timeout TO '%ds'" % STATEMENT_TIMEOUT)
+          yield
+        ensure
+          execute('RESET statement_timeout')
+        end
+
+        delegate :execute, :quote_table_name, to: :connection
+        def connection
+          @connection ||= ActiveRecord::Base.connection
+        end
+      end
+    end
+  end
+end

spec/db/schema_spec.rb

@@ -264,6 +264,18 @@ RSpec.describe 'Database schema' do
     end
   end
 
+  context 'index names' do
+    it 'disallows index names with a _ccnew[0-9]* suffix' do
+      # During REINDEX operations, Postgres generates a temporary index with a _ccnew[0-9]* suffix
+      # Since indexes are being considered temporary and subject to removal if they stick around for longer. See Gitlab::Database::Reindexing.
+      #
+      # Hence we disallow adding permanent indexes with this suffix.
+      problematic_indexes = Gitlab::Database::PostgresIndex.match("#{Gitlab::Database::Reindexing::ReindexConcurrently::TEMPORARY_INDEX_PATTERN}$").all
+
+      expect(problematic_indexes).to be_empty
+    end
+  end
+
   private
 
   def retrieve_columns_name_with_jsonb

spec/lib/gitlab/database/postgres_index_spec.rb

@@ -34,6 +34,24 @@ RSpec.describe Gitlab::Database::PostgresIndex do
     it 'only indexes that dont serve an exclusion constraint' do
       expect(described_class.regular).to all(have_attributes(exclusion: false))
     end
+
+    it 'only non-expression indexes' do
+      expect(described_class.regular).to all(have_attributes(expression: false))
+    end
+  end
+
+  describe '.reindexing_support' do
+    it 'only non partitioned indexes' do
+      expect(described_class.reindexing_support).to all(have_attributes(partitioned: false))
+    end
+
+    it 'only indexes that dont serve an exclusion constraint' do
+      expect(described_class.reindexing_support).to all(have_attributes(exclusion: false))
+    end
+
+    it 'only non-expression indexes' do
+      expect(described_class.reindexing_support).to all(have_attributes(expression: false))
+    end
   end
 
   describe '.not_match' do

spec/lib/gitlab/database/reindexing/coordinator_spec.rb

@@ -9,13 +9,6 @@ RSpec.describe Gitlab::Database::Reindexing::Coordinator do
   describe '.perform' do
     subject { described_class.new(index, notifier).perform }
 
-    before do
-      swapout_view_for_table(:postgres_indexes)
-
-      allow(Gitlab::Database::Reindexing::ConcurrentReindex).to receive(:new).with(index).and_return(reindexer)
-      allow(Gitlab::Database::Reindexing::ReindexAction).to receive(:create_for).with(index).and_return(action)
-    end
-
     let(:index) { create(:postgres_index) }
     let(:notifier) { instance_double(Gitlab::Database::Reindexing::GrafanaNotifier, notify_start: nil, notify_end: nil) }
     let(:reindexer) { instance_double(Gitlab::Database::Reindexing::ConcurrentReindex, perform: nil) }
@@ -26,6 +19,7 @@ RSpec.describe Gitlab::Database::Reindexing::Coordinator do
     let(:lease_timeout) { 1.day }
     let(:uuid) { 'uuid' }
 
+    shared_examples_for 'reindexing coordination' do
       context 'locking' do
         it 'acquires a lock while reindexing' do
           expect(lease).to receive(:try_obtain).ordered.and_return(uuid)
@@ -79,4 +73,29 @@ RSpec.describe Gitlab::Database::Reindexing::Coordinator do
         end
       end
     end
+
+    context 'legacy reindexing method (< PG12) - to be removed' do
+      before do
+        stub_feature_flags(database_reindexing_pg12: false)
+        swapout_view_for_table(:postgres_indexes)
+
+        allow(Gitlab::Database::Reindexing::ConcurrentReindex).to receive(:new).with(index).and_return(reindexer)
+        allow(Gitlab::Database::Reindexing::ReindexAction).to receive(:create_for).with(index).and_return(action)
+      end
+
+      it_behaves_like 'reindexing coordination'
+    end
+
+    context 'PG12 reindexing method' do
+      before do
+        stub_feature_flags(database_reindexing_pg12: true)
+        swapout_view_for_table(:postgres_indexes)
+
+        allow(Gitlab::Database::Reindexing::ReindexConcurrently).to receive(:new).with(index).and_return(reindexer)
+        allow(Gitlab::Database::Reindexing::ReindexAction).to receive(:create_for).with(index).and_return(action)
+      end
+
+      it_behaves_like 'reindexing coordination'
+    end
+  end
 end

spec/lib/gitlab/database/reindexing/reindex_concurrently_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Database::Reindexing::ReindexConcurrently, '#perform' do
+  subject { described_class.new(index, logger: logger).perform }
+
+  let(:table_name) { '_test_reindex_table' }
+  let(:column_name) { '_test_column' }
+  let(:index_name) { '_test_reindex_index' }
+  let(:index) { Gitlab::Database::PostgresIndex.by_identifier("public.#{iname(index_name)}") }
+  let(:logger) { double('logger', debug: nil, info: nil, error: nil ) }
+  let(:connection) { ActiveRecord::Base.connection }
+
+  before do
+    connection.execute(<<~SQL)
+      CREATE TABLE #{table_name} (
+        id serial NOT NULL PRIMARY KEY,
+        #{column_name} integer NOT NULL);
+
+      CREATE INDEX #{index_name} ON #{table_name} (#{column_name});
+    SQL
+  end
+
+  context 'when the index serves an exclusion constraint' do
+    before do
+      allow(index).to receive(:exclusion?).and_return(true)
+    end
+
+    it 'raises an error' do
+      expect { subject }.to raise_error(described_class::ReindexError, /indexes serving an exclusion constraint are currently not supported/)
+    end
+  end
+
+  context 'when attempting to reindex an expression index' do
+    before do
+      allow(index).to receive(:expression?).and_return(true)
+    end
+
+    it 'raises an error' do
+      expect { subject }.to raise_error(described_class::ReindexError, /expression indexes are currently not supported/)
+    end
+  end
+
+  context 'when the index is a dangling temporary index from a previous reindexing run' do
+    context 'with the temporary index prefix' do
+      let(:index_name) { '_test_reindex_index_ccnew' }
+
+      it 'raises an error' do
+        expect { subject }.to raise_error(described_class::ReindexError, /left-over temporary index/)
+      end
+    end
+
+    context 'with the temporary index prefix with a counter' do
+      let(:index_name) { '_test_reindex_index_ccnew1' }
+
+      it 'raises an error' do
+        expect { subject }.to raise_error(described_class::ReindexError, /left-over temporary index/)
+      end
+    end
+  end
+
+  it 'recreates the index using REINDEX with a long statement timeout' do
+    expect_to_execute_in_order(
+      "SET statement_timeout TO '32400s'",
+      "REINDEX INDEX CONCURRENTLY \"public\".\"#{index.name}\"",
+      "RESET statement_timeout"
+    )
+
+    subject
+  end
+
+  context 'with dangling indexes matching TEMPORARY_INDEX_PATTERN, i.e. /some\_index\_ccnew(\d)*/' do
+    before do
+      # dangling indexes
+      connection.execute("CREATE INDEX #{iname(index_name, '_ccnew')} ON #{table_name} (#{column_name})")
+      connection.execute("CREATE INDEX #{iname(index_name, '_ccnew2')} ON #{table_name} (#{column_name})")
+
+      # Unrelated index - don't drop
+      connection.execute("CREATE INDEX some_other_index_ccnew ON #{table_name} (#{column_name})")
+    end
+
+    shared_examples_for 'dropping the dangling index' do
+      it 'drops the dangling indexes while controlling lock_timeout' do
+        expect_to_execute_in_order(
+          # Regular index rebuild
+          "SET statement_timeout TO '32400s'",
+          "REINDEX INDEX CONCURRENTLY \"public\".\"#{index_name}\"",
+          "RESET statement_timeout",
+          # Drop _ccnew index
+          "SET lock_timeout TO '60000ms'",
+          "DROP INDEX CONCURRENTLY IF EXISTS \"public\".\"#{iname(index_name, '_ccnew')}\"",
+          "RESET idle_in_transaction_session_timeout; RESET lock_timeout",
+          # Drop _ccnew2 index
+          "SET lock_timeout TO '60000ms'",
+          "DROP INDEX CONCURRENTLY IF EXISTS \"public\".\"#{iname(index_name, '_ccnew2')}\"",
+          "RESET idle_in_transaction_session_timeout; RESET lock_timeout"
+        )
+
+        subject
+      end
+    end
+
+    context 'with normal index names' do
+      it_behaves_like 'dropping the dangling index'
+    end
+
+    context 'with index name at 63 character limit' do
+      let(:index_name) { 'a' * 63 }
+
+      before do
+        # Another unrelated index - don't drop
+        extra_index = index_name[0...55]
+        connection.execute("CREATE INDEX #{extra_index}_ccnew ON #{table_name} (#{column_name})")
+      end
+
+      it_behaves_like 'dropping the dangling index'
+    end
+  end
+
+  def iname(name, suffix = '')
+    "#{name[0...63 - suffix.size]}#{suffix}"
+  end
+
+  def expect_to_execute_in_order(*queries)
+    # Indexes cannot be created CONCURRENTLY in a transaction. Since the tests are wrapped in transactions,
+    # verify the original call but pass through the non-concurrent form.
+    queries.each do |query|
+      expect(connection).to receive(:execute).with(query).ordered.and_wrap_original do |method, sql|
+        method.call(sql.sub(/CONCURRENTLY/, ''))
+      end
+    end
+  end
+end

spec/lib/gitlab/database/reindexing_spec.rb

@@ -29,11 +29,30 @@ RSpec.describe Gitlab::Database::Reindexing do
   describe '.candidate_indexes' do
     subject { described_class.candidate_indexes }
 
+    context 'with deprecated method for < PG12' do
+      before do
+        stub_feature_flags(database_reindexing_pg12: false)
+      end
+
+      it 'retrieves regular indexes that are no left-overs from previous runs' do
+        result = double
+        expect(Gitlab::Database::PostgresIndex).to receive_message_chain('not_match.not_match.not_match.regular').with('^tmp_reindex_').with('^old_reindex_').with('\_ccnew[0-9]*$').with(no_args).and_return(result)
+
+        expect(subject).to eq(result)
+      end
+    end
+
+    context 'with deprecated method for >= PG12' do
+      before do
+        stub_feature_flags(database_reindexing_pg12: true)
+      end
+
       it 'retrieves regular indexes that are no left-overs from previous runs' do
         result = double
-      expect(Gitlab::Database::PostgresIndex).to receive_message_chain('regular.where.not_match.not_match').with(no_args).with('NOT expression').with('^tmp_reindex_').with('^old_reindex_').and_return(result)
+        expect(Gitlab::Database::PostgresIndex).to receive_message_chain('not_match.not_match.not_match.reindexing_support').with('^tmp_reindex_').with('^old_reindex_').with('\_ccnew[0-9]*$').with(no_args).and_return(result)
 
         expect(subject).to eq(result)
       end
     end
+  end
 end