Add support for UNLOGGED Postgresql tables

This commit adds support for the
`ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables`
setting, which turns `CREATE TABLE` SQL statements into
`CREATE UNLOGGED TABLE` statements.

This can improve PostgreSQL performance but at the
cost of data durability, and thus it is highly recommended
that you *DO NOT* enable this in a production environment.

activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb

@@ -39,7 +39,7 @@ module ActiveRecord
           end
 
           def visit_TableDefinition(o)
-            create_sql = +"CREATE#{' TEMPORARY' if o.temporary} TABLE "
+            create_sql = +"CREATE#{table_modifier_in_create(o)} TABLE "
             create_sql << "IF NOT EXISTS " if o.if_not_exists
             create_sql << "#{quote_table_name(o.name)} "
 
@@ -121,6 +121,11 @@ module ActiveRecord
             sql
           end
 
+          # Returns any SQL string to go between CREATE and TABLE. May be nil.
+          def table_modifier_in_create(o)
+            " TEMPORARY" if o.temporary
+          end
+
           def foreign_key_in_create(from_table, to_table, options)
             options = foreign_key_options(from_table, to_table, options)
             accept ForeignKeyDefinition.new(from_table, to_table, options)

activerecord/lib/active_record/connection_adapters/postgresql/schema_creation.rb

@@ -23,6 +23,17 @@ module ActiveRecord
             end
             super
           end
+
+          # Returns any SQL string to go between CREATE and TABLE. May be nil.
+          def table_modifier_in_create(o)
+            # A table cannot be both TEMPORARY and UNLOGGED, since all TEMPORARY
+            # tables are already UNLOGGED.
+            if o.temporary
+              " TEMPORARY"
+            elsif o.unlogged
+              " UNLOGGED"
+            end
+          end
       end
     end
   end

activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb

@@ -175,6 +175,13 @@ module ActiveRecord
       class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
         include ColumnMethods
 
+        attr_reader :unlogged
+
+        def initialize(*)
+          super
+          @unlogged = ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables
+        end
+
         private
           def integer_like_primary_key_type(type, options)
             if type == :bigint || options[:limit] == 8

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -85,6 +85,18 @@ module ActiveRecord
     class PostgreSQLAdapter < AbstractAdapter
       ADAPTER_NAME = "PostgreSQL"
 
+      ##
+      # :singleton-method:
+      # PostgreSQL allows the creation of "unlogged" tables, which do not record
+      # data in the PostgreSQL Write-Ahead Log. This can make the tables faster,
+      # bug significantly increases the risk of data loss if the database
+      # crashes. As a result, this should not be used in production
+      # environments. If you would like all created tables to be unlogged you
+      # can add the following line to your test.rb file:
+      #
+      #   ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = true
+      class_attribute :create_unlogged_tables, default: false
+
       NATIVE_DATABASE_TYPES = {
         primary_key: "bigserial primary key",
         string:      { name: "character varying" },

activerecord/test/cases/adapters/postgresql/create_unlogged_tables_test.rb

@@ -0,0 +1,74 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/schema_dumping_helper"
+
+class UnloggedTablesTest < ActiveRecord::PostgreSQLTestCase
+  include SchemaDumpingHelper
+
+  TABLE_NAME = "things"
+  LOGGED_FIELD = "relpersistence"
+  LOGGED_QUERY = "SELECT #{LOGGED_FIELD} FROM pg_class WHERE relname = '#{TABLE_NAME}'"
+  LOGGED = "p"
+  UNLOGGED = "u"
+  TEMPORARY = "t"
+
+  class Thing < ActiveRecord::Base
+    self.table_name = TABLE_NAME
+  end
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = false
+  end
+
+  teardown do
+    @connection.drop_table TABLE_NAME, if_exists: true
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = false
+  end
+
+  def test_logged_by_default
+    @connection.create_table(TABLE_NAME) do |t|
+    end
+    assert_equal @connection.execute(LOGGED_QUERY).first[LOGGED_FIELD], LOGGED
+  end
+
+  def test_unlogged_in_test_environment_when_unlogged_setting_enabled
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = true
+
+    @connection.create_table(TABLE_NAME) do |t|
+    end
+    assert_equal @connection.execute(LOGGED_QUERY).first[LOGGED_FIELD], UNLOGGED
+  end
+
+  def test_not_included_in_schema_dump
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = true
+
+    @connection.create_table(TABLE_NAME) do |t|
+    end
+    assert_no_match(/unlogged/i, dump_table_schema(TABLE_NAME))
+  end
+
+  def test_not_changed_in_change_table
+    @connection.create_table(TABLE_NAME) do |t|
+    end
+
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = true
+
+    @connection.change_table(TABLE_NAME) do |t|
+      t.column :name, :string
+    end
+    assert_equal @connection.execute(LOGGED_QUERY).first[LOGGED_FIELD], LOGGED
+  end
+
+  def test_gracefully_handles_temporary_tables
+    @connection.create_table(TABLE_NAME, temporary: true) do |t|
+    end
+
+    # Temporary tables are already unlogged, though this query results in a
+    # different result ("t" vs. "u"). This test is really just checking that we
+    # didn't try to run `CREATE TEMPORARY UNLOGGED TABLE`, which would result in
+    # a PostgreSQL error.
+    assert_equal @connection.execute(LOGGED_QUERY).first[LOGGED_FIELD], TEMPORARY
+  end
+end

guides/source/configuring.md

@@ -379,6 +379,14 @@ The MySQL adapter adds one additional configuration option:
 
 * `ActiveRecord::ConnectionAdapters::Mysql2Adapter.emulate_booleans` controls whether Active Record will consider all `tinyint(1)` columns as booleans. Defaults to `true`.
 
+The PostgreSQL adapter adds one additional configuration option:
+
+* `ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables`
+  controls whether database tables created should be "unlogged," which can speed
+  up performance but adds a risk of data loss if the database crashes. It is
+  highly recommended that you do not enable this in a production environment.
+  Defaults to `false` in all environments.
+
 The SQLite3Adapter adapter adds one additional configuration option:
 
 * `ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer`