Raise specific exception on Mysql2::Error::TimeoutError

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -619,7 +619,11 @@ module ActiveRecord
           when ER_QUERY_INTERRUPTED
             QueryCanceled.new(message, sql: sql, binds: binds)
           else
-            super
+            if exception.is_a?(Mysql2::Error::TimeoutError)
+              ActiveRecord::AdapterTimeout.new(message, sql: sql, binds: binds)
+            else
+              super
+            end
           end
         end
 

activerecord/lib/active_record/errors.rb

@@ -365,6 +365,10 @@ module ActiveRecord
   class QueryCanceled < StatementInvalid
   end
 
+  # AdapterTimeout will be raised when database clients times out while waiting from the server
+  class AdapterTimeout < StatementInvalid
+  end
+
   # UnknownAttributeReference is raised when an unknown and potentially unsafe
   # value is passed to a query method when allow_unsafe_raw_sql is set to
   # :disabled. For example, passing a non column name value to a relation's

activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb

@@ -225,6 +225,20 @@ class Mysql2AdapterTest < ActiveRecord::Mysql2TestCase
     end
   end
 
+  def test_read_timeout_exception
+    ActiveRecord::Base.establish_connection(
+      ActiveRecord::Base.configurations[:arunit].merge("read_timeout" => 1)
+    )
+
+    error = assert_raises(ActiveRecord::AdapterTimeout) do
+      ActiveRecord::Base.connection.execute("SELECT SLEEP(2)")
+    end
+
+    assert_equal Mysql2::Error::TimeoutError, error.cause.class
+  ensure
+    ActiveRecord::Base.establish_connection :arunit
+  end
+
   private
     def with_example_table(definition = "id int auto_increment primary key, number int, data varchar(255)", &block)
       super(@conn, "ex", definition, &block)