Make `truncate_tables` to bulk statements

Before:

```
   (16.4ms)  TRUNCATE TABLE `author_addresses`
   (20.5ms)  TRUNCATE TABLE `authors`
   (19.4ms)  TRUNCATE TABLE `posts`
```

After:

```
  Truncate Tables (19.5ms)  TRUNCATE TABLE `author_addresses`;
TRUNCATE TABLE `authors`;
TRUNCATE TABLE `posts`
```

9 files changed, 123 insertions, 59 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index bfd1c8402c..0cf0290770 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -144,11 +144,20 @@ module ActiveRecord
 
       # Executes the truncate statement.
       def truncate(table_name, name = nil)
-        execute "TRUNCATE TABLE #{quote_table_name(table_name)}", name
+        execute(build_truncate_statements(table_name), name)
       end
 
       def truncate_tables(*table_names) # :nodoc:
-        table_names.each { |table_name| truncate(table_name) }
+        unless table_names.empty?
+          with_multi_statements do
+            disable_referential_integrity do
+              Array(build_truncate_statements(*table_names)).each do |sql|
+                execute_batch(sql, "Truncate Tables")
+                yield if block_given?
+              end
+            end
+          end
+        end
       end
 
       # Executes update +sql+ statement in the context of this connection using
@@ -378,13 +387,15 @@ module ActiveRecord
         end.compact
 
         table_deletes = tables_to_delete.map { |table| +"DELETE FROM #{quote_table_name table}" }
-        total_sql = Array.wrap(combine_multi_statements(table_deletes + fixture_inserts))
-
-        disable_referential_integrity do
-          transaction(requires_new: true) do
-            total_sql.each do |sql|
-              execute sql, "Fixtures Load"
-              yield if block_given?
+        total_sql = Array(combine_multi_statements(table_deletes + fixture_inserts))
+
+        with_multi_statements do
+          disable_referential_integrity do
+            transaction(requires_new: true) do
+              total_sql.each do |sql|
+                execute_batch(sql, "Fixtures Load")
+                yield if block_given?
+              end
             end
           end
         end
@@ -420,6 +431,10 @@ module ActiveRecord
       end
 
       private
+        def execute_batch(sql, name = nil)
+          execute(sql, name)
+        end
+
         def default_insert_value(column)
           Arel.sql("DEFAULT")
         end
@@ -455,6 +470,17 @@ module ActiveRecord
           manager.to_sql
         end
 
+        def build_truncate_statements(*table_names)
+          truncate_tables = table_names.map do |table_name|
+            "TRUNCATE TABLE #{quote_table_name(table_name)}"
+          end
+          combine_multi_statements(truncate_tables)
+        end
+
+        def with_multi_statements
+          yield
+        end
+
         def combine_multi_statements(total_sql)
           total_sql.join(";\n")
         end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 5ceddf449c..8ca2cfa9ed 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -512,12 +512,6 @@ module ActiveRecord
         index.using == :btree || super
       end
 
-      def insert_fixtures_set(fixture_set, tables_to_delete = [])
-        with_multi_statements do
-          super { discard_remaining_results }
-        end
-      end
-
       def build_insert_sql(insert) # :nodoc:
         sql = +"INSERT #{insert.into} #{insert.values_list}"
 
@@ -539,33 +533,6 @@ module ActiveRecord
           end
         end
 
-        def combine_multi_statements(total_sql)
-          total_sql.each_with_object([]) do |sql, total_sql_chunks|
-            previous_packet = total_sql_chunks.last
-            sql << ";\n"
-            if max_allowed_packet_reached?(sql, previous_packet) || total_sql_chunks.empty?
-              total_sql_chunks << sql
-            else
-              previous_packet << sql
-            end
-          end
-        end
-
-        def max_allowed_packet_reached?(current_packet, previous_packet)
-          if current_packet.bytesize > max_allowed_packet
-            raise ActiveRecordError, "Fixtures set is too large #{current_packet.bytesize}. Consider increasing the max_allowed_packet variable."
-          elsif previous_packet.nil?
-            false
-          else
-            (current_packet.bytesize + previous_packet.bytesize) > max_allowed_packet
-          end
-        end
-
-        def max_allowed_packet
-          bytes_margin = 2
-          @max_allowed_packet ||= (show_variable("max_allowed_packet") - bytes_margin)
-        end
-
         def initialize_type_map(m = type_map)
           super
 
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
index 6adcc14545..421afc34bc 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
@@ -68,6 +68,14 @@ module ActiveRecord
         end
         alias :exec_update :exec_delete
 
+        def insert_fixtures_set(fixture_set, tables_to_delete = []) # :nodoc:
+          super { discard_remaining_results }
+        end
+
+        def truncate_tables(*table_names) # :nodoc:
+          super { discard_remaining_results }
+        end
+
         private
           def default_insert_value(column)
             Arel.sql("DEFAULT") unless column.auto_increment?
@@ -85,6 +93,14 @@ module ActiveRecord
             @connection.respond_to?(:set_server_option)
           end
 
+          def build_truncate_statements(*table_names)
+            if table_names.size == 1
+              super.first
+            else
+              super
+            end
+          end
+
           def multi_statements_enabled?(flags)
             if flags.is_a?(Array)
               flags.include?("MULTI_STATEMENTS")
@@ -117,6 +133,36 @@ module ActiveRecord
             end
           end
 
+          def combine_multi_statements(total_sql)
+            total_sql.each_with_object([]) do |sql, total_sql_chunks|
+              previous_packet = total_sql_chunks.last
+              if max_allowed_packet_reached?(sql, previous_packet)
+                total_sql_chunks << +sql
+              else
+                previous_packet << ";\n"
+                previous_packet << sql
+              end
+            end
+          end
+
+          def max_allowed_packet_reached?(current_packet, previous_packet)
+            if current_packet.bytesize > max_allowed_packet
+              raise ActiveRecordError,
+                "Fixtures set is too large #{current_packet.bytesize}. Consider increasing the max_allowed_packet variable."
+            elsif previous_packet.nil?
+              true
+            else
+              (current_packet.bytesize + previous_packet.bytesize) > max_allowed_packet
+            end
+          end
+
+          def max_allowed_packet
+            @max_allowed_packet ||= begin
+              bytes_margin = 2
+              show_variable("max_allowed_packet") - bytes_margin
+            end
+          end
+
           def exec_stmt_and_free(sql, name, binds, cache_stmt: false)
             if preventing_writes? && write_query?(sql)
               raise ActiveRecord::ReadOnlyError, "Write query attempted while in readonly mode: #{sql}"
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
index 208934385f..ae7dbd2868 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
@@ -143,12 +143,6 @@ module ActiveRecord
           end
         end
 
-        def truncate_tables(*table_names) # :nodoc:
-          unless table_names.empty?
-            execute "TRUNCATE TABLE #{table_names.map(&method(:quote_table_name)).join(", ")}"
-          end
-        end
-
         # Begins a transaction.
         def begin_db_transaction
           execute "BEGIN"
@@ -170,6 +164,10 @@ module ActiveRecord
         end
 
         private
+          def build_truncate_statements(*table_names)
+            "TRUNCATE TABLE #{table_names.map(&method(:quote_table_name)).join(", ")}"
+          end
+
           # Returns the current ID of a table's sequence.
           def last_insert_id_result(sequence_name)
             exec_query("SELECT currval(#{quote(sequence_name)})", "SQL")
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/database_statements.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/database_statements.rb
new file mode 100644
index 0000000000..64ef53e2e4
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/database_statements.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module SQLite3
+      module DatabaseStatements
+        private
+          def execute_batch(sql, name = nil)
+            if preventing_writes? && write_query?(sql)
+              raise ActiveRecord::ReadOnlyError, "Write query attempted while in readonly mode: #{sql}"
+            end
+
+            materialize_transactions
+
+            log(sql, name) do
+              ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+                @connection.execute_batch(sql)
+              end
+            end
+          end
+
+          def build_truncate_statements(*table_names)
+            truncate_tables = table_names.map do |table_name|
+              "DELETE FROM #{quote_table_name(table_name)}"
+            end
+            combine_multi_statements(truncate_tables)
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 8ee7e4c763..30b69c1e60 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -4,6 +4,7 @@ require "active_record/connection_adapters/abstract_adapter"
 require "active_record/connection_adapters/statement_pool"
 require "active_record/connection_adapters/sqlite3/explain_pretty_printer"
 require "active_record/connection_adapters/sqlite3/quoting"
+require "active_record/connection_adapters/sqlite3/database_statements"
 require "active_record/connection_adapters/sqlite3/schema_creation"
 require "active_record/connection_adapters/sqlite3/schema_definitions"
 require "active_record/connection_adapters/sqlite3/schema_dumper"
@@ -58,6 +59,7 @@ module ActiveRecord
 
       include SQLite3::Quoting
       include SQLite3::SchemaStatements
+      include SQLite3::DatabaseStatements
 
       NATIVE_DATABASE_TYPES = {
         primary_key:  "integer PRIMARY KEY AUTOINCREMENT NOT NULL",
@@ -275,10 +277,6 @@ module ActiveRecord
         end
       end
 
-      def truncate(table_name, name = nil) # :nodoc:
-        execute "DELETE FROM #{quote_table_name(table_name)}", name
-      end
-
       def begin_db_transaction #:nodoc:
         log("begin transaction", nil) { @connection.transaction }
       end
diff --git a/activerecord/lib/active_record/tasks/database_tasks.rb b/activerecord/lib/active_record/tasks/database_tasks.rb
index 5a46003732..f18990cc5b 100644
--- a/activerecord/lib/active_record/tasks/database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/database_tasks.rb
@@ -190,9 +190,7 @@ module ActiveRecord
             ActiveRecord::Base.internal_metadata_table_name
           ]
 
-          ActiveRecord::Base.connection.disable_referential_integrity do
-            ActiveRecord::Base.connection.truncate_tables(*table_names)
-          end unless table_names.empty?
+          ActiveRecord::Base.connection.truncate_tables(*table_names) unless table_names.empty?
         end
       end
       private :truncate_tables
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index d25faf21d8..2b20d842e8 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -493,13 +493,13 @@ module ActiveRecord
     end
 
     def test_truncate_tables
+      assert_operator @connection.query_value("SELECT COUNT(*) FROM posts"), :>, 0
       assert_operator @connection.query_value("SELECT COUNT(*) FROM authors"), :>, 0
       assert_operator @connection.query_value("SELECT COUNT(*) FROM author_addresses"), :>, 0
 
-      @connection.disable_referential_integrity do
-        @connection.truncate_tables("author_addresses", "authors")
-      end
+      @connection.truncate_tables("author_addresses", "authors", "posts")
 
+      assert_equal 0, @connection.query_value("SELECT COUNT(*) FROM posts")
       assert_equal 0, @connection.query_value("SELECT COUNT(*) FROM authors")
       assert_equal 0, @connection.query_value("SELECT COUNT(*) FROM author_addresses")
     end
diff --git a/activerecord/test/cases/fixtures_test.rb b/activerecord/test/cases/fixtures_test.rb
index b4f28fbfd6..0c8263c9fd 100644
--- a/activerecord/test/cases/fixtures_test.rb
+++ b/activerecord/test/cases/fixtures_test.rb
@@ -209,7 +209,7 @@ class FixturesTest < ActiveRecord::TestCase
       conn = ActiveRecord::Base.connection
       mysql_margin = 2
       packet_size = 1024
-      bytes_needed_to_have_a_1024_bytes_fixture = 858
+      bytes_needed_to_have_a_1024_bytes_fixture = 860
       fixtures = {
         "traffic_lights" => [
           { "location" => "US", "state" => ["NY"], "long_state" => ["a" * bytes_needed_to_have_a_1024_bytes_fixture] },