openproject/config/initializers/enforce_isolation_level.rb

#-- encoding: UTF-8
#-- copyright
# OpenProject is a project management system.
# Copyright (C) 2012-2015 the OpenProject Foundation (OPF)
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License version 3.
#
# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
# Copyright (C) 2006-2013 Jean-Philippe Lang
# Copyright (C) 2010-2013 the ChiliProject Team
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
#
# See doc/COPYRIGHT.rdoc for more details.
#++

# We need to ensure that we operate on a well-known TRANSACTION ISOLATION LEVEL
# However, the default isolation level is different for MySQL and PostgreSQL and it is also
# possible (at least for MySQL) to globally override the default for your DBMS installation.
# Therefore we want to ensure that the isolation level is consistent on a session basis.
# We chose READ COMMITTED as our expected default isolation level, this is the default of
# PostgreSQL.
module ConnectionIsolationLevel
  module ConnectionPoolPatch
    def new_connection
      connection = super
      ConnectionIsolationLevel.set_connection_isolation_level connection
      connection
    end
  end

  def self.set_connection_isolation_level(connection)
    isolation_level = 'ISOLATION LEVEL READ COMMITTED'
    if OpenProject::Database.mysql?(connection)
      connection.execute("SET SESSION TRANSACTION #{isolation_level}")
    else
      connection.execute("SET SESSION CHARACTERISTICS AS TRANSACTION #{isolation_level}")
    end
  end
end

ActiveRecord::ConnectionAdapters::ConnectionPool.send(:prepend,
                                                      ConnectionIsolationLevel::ConnectionPoolPatch)

# in case the existing connection was created before our patch
# N.B.: this assumes that our process only has this single thread, which is at least true today...
ConnectionIsolationLevel.set_connection_isolation_level ActiveRecord::Base.connection