title: peewee PooledMySQLDatabase has cache or buffer?
body: <p>i create a mysql connection pool like this:</p>
  
  <pre><code>database = PooledMySQLDatabase('test', max_connections=10,
                         **{'host': 'localhost', 'port': 3306,
                            'user': 'root', 'password': ''})
  
  
  class BaseModel(Model):
  class Meta:
      database = database
  
  
  
  class Tb1(BaseModel):
      point_id = PrimaryKeyField()
  
      class Meta:
          db_table = 'tb1'
  </code></pre>
  
  <p>however, where i insert a record or delete a record in database manully, in my program, select result is not change.</p>
  
  <pre><code>while True:
      database.connect()
      tb_list = Tb1.select()
      print(len(tb_list))
      database.close()
      import time
      time.sleep(2)
  </code></pre>
  
  <p>when i repalce PooledMySQLDatabase to MySQLDatabase the result is normal.
  In my project, I want to use multithread, so I need to create a mysql pool.</p>
  
  <p>thanks a lot</p>