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.

4 files changed, 36 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
index 19ff780192..2cb0a2a4df 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
+++ b/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)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_creation.rb
index 8e381a92cf..ceb8b40bd9 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_creation.rb
+++ b/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
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
index 206b855a18..dc4a0bb26e 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
+++ b/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
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index a11a786ec7..f701292be3 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/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" },