Introduce new ActiveRecord transaction error classes

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -742,7 +742,7 @@ def translate_exception(exception, message)
         when ER_DATA_TOO_LONG
           ValueTooLong.new(message)
         when ER_LOCK_DEADLOCK
-          TransactionSerializationError.new(message)
+          DeadlockDetected.new(message)
         else
           super
         end

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -407,6 +407,7 @@ def postgresql_version
         FOREIGN_KEY_VIOLATION = "23503"
         UNIQUE_VIOLATION      = "23505"
         SERIALIZATION_FAILURE = "40001"
+        DEADLOCK_DETECTED     = "40P01"
 
         def translate_exception(exception, message)
           return exception unless exception.respond_to?(:result)
@@ -419,7 +420,9 @@ def translate_exception(exception, message)
           when VALUE_LIMIT_VIOLATION
             ValueTooLong.new(message)
           when SERIALIZATION_FAILURE
-            TransactionSerializationError.new(message)
+            SerializationFailure.new(message)
+          when DEADLOCK_DETECTED
+            DeadlockDetected.new(message)
           else
             super
           end

activerecord/lib/active_record/errors.rb

@@ -285,14 +285,24 @@ class ImmutableRelation < ActiveRecordError
   class TransactionIsolationError < ActiveRecordError
   end
 
-  # TransactionSerializationError will be raised when a transaction is rolled
+  # TransactionRollbackError will be raised when a transaction is rolled
   # back by the database due to a serialization failure or a deadlock.
   #
   # See the following:
   #
   # * http://www.postgresql.org/docs/current/static/transaction-iso.html
   # * https://dev.mysql.com/doc/refman/5.7/en/error-messages-server.html#error_er_lock_deadlock
-  class TransactionSerializationError < ActiveRecordError
+  class TransactionRollbackError < ActiveRecordError
+  end
+
+  # SerializationFailure will be raised when a transaction is rolled
+  # back by the database due to a serialization failure.
+  class SerializationFailure < TransactionRollbackError
+  end
+
+  # DeadlockDetected will be raised when a transaction is rolled
+  # back by the database when a deadlock is encountered.
+  class DeadlockDetected < TransactionRollbackError
   end
 
   # IrreversibleOrderError is raised when a relation's order is too complex for

activerecord/test/cases/adapters/mysql2/transaction_test.rb

@@ -27,32 +27,25 @@ class Sample < ActiveRecord::Base
       @connection.drop_table 'samples', if_exists: true
     end
 
-    test "raises error when a serialization failure occurs" do
-      assert_raises(ActiveRecord::TransactionSerializationError) do
-        thread = Thread.new do
-          Sample.transaction isolation: :serializable do
-            Sample.delete_all
-
-            10.times do |i|
-              sleep 0.1
+    test "raises DeadlockDetected when a deadlock is encountered" do
+      assert_raises(ActiveRecord::DeadlockDetected) do
+        s1 = Sample.create value: 1
+        s2 = Sample.create value: 2
 
-              Sample.create value: i
-            end
+        thread = Thread.new do
+          Sample.transaction do
+            s1.lock!
+            sleep 1
+            s2.update_attributes value: 1
           end
         end
 
-        sleep 0.1
-
-        Sample.transaction isolation: :serializable do
-          Sample.delete_all
-
-          10.times do |i|
-            sleep 0.1
-
-            Sample.create value: i
-          end
+        sleep 0.5
 
+        Sample.transaction do
+          s2.lock!
           sleep 1
+          s1.update_attributes value: 2
         end
 
         thread.join

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

@@ -26,9 +26,9 @@ class Sample < ActiveRecord::Base
       @connection.drop_table 'samples', if_exists: true
     end
 
-    test "raises error when a serialization failure occurs" do
+    test "raises SerializationFailure when a serialization failure occurs" do
       with_warning_suppression do
-        assert_raises(ActiveRecord::TransactionSerializationError) do
+        assert_raises(ActiveRecord::SerializationFailure) do
           thread = Thread.new do
             Sample.transaction isolation: :serializable do
               Sample.delete_all
@@ -51,8 +51,33 @@ class Sample < ActiveRecord::Base
 
               Sample.create value: i
             end
+          end
+
+          thread.join
+        end
+      end
+    end
+
+    test "raises DeadlockDetected when a deadlock is encountered" do
+      with_warning_suppression do
+        assert_raises(ActiveRecord::DeadlockDetected) do
+          s1 = Sample.create value: 1
+          s2 = Sample.create value: 2
+
+          thread = Thread.new do
+            Sample.transaction do
+              s1.lock!
+              sleep 1
+              s2.update_attributes value: 1
+            end
+          end
+
+          sleep 0.5
 
+          Sample.transaction do
+            s2.lock!
             sleep 1
+            s1.update_attributes value: 2
           end
 
           thread.join