Re-land https://codereview.chromium.org/2102003003/

third_party/buildbot_8_4p1/buildbot/db/enginestrategy.py

 # This file is part of Buildbot.  Buildbot 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, version 2.
 #
 # 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
@@ skipping 64 matching lines @@
 
             u.database = u.database % dict(basedir = kwargs['basedir'])
             if not os.path.isabs(u.database[0]):
                 u.database = os.path.join(kwargs['basedir'], u.database)
 
         # in-memory databases need exactly one connection
         if not u.database:
             kwargs['pool_size'] = 1
             max_conns = 1
 
-        # allow serializing access to the db
-        if 'serialize_access' in u.query:
-            u.query.pop('serialize_access')
-            max_conns = 1
-
         return u, kwargs, max_conns
 
     def set_up_sqlite_engine(self, u, engine):
         """Special setup for sqlite engines"""
         # try to enable WAL logging
         if u.database:
             log.msg("setting database journal mode to 'wal'")
             try:
                 engine.execute("pragma journal_mode = wal")
             except:
@@ skipping 74 matching lines @@
 
 BuildbotEngineStrategy()
 
 # this module is really imported for the side-effects, but pyflakes will like
 # us to use something from the module -- so offer a copy of create_engine, which
 # explicitly adds the strategy argument
 def create_engine(*args, **kwargs):
     kwargs['strategy'] = 'buildbot'
 
     return sqlalchemy.create_engine(*args, **kwargs)