## Impacted versions:
 8.0 / 9.0 / 10.0
## Steps to reproduce:
* see https://github.com/odoo/odoo/issues/11841
* in a shell
  1. create an in memory record `order = self.env['purcahse.order'].new({....})`
  2. create an in memory record with a reference to the first one `order_line = self.env['purchase.order.line'].new({'order_id': order, ....})`
  3. order_line.order_id is an in memory recordset
  4. create a record for a model that inherits from mail.thread `self.env['product.product'].create({....})`
  5. At this stage order_line.order_id is an empty recordset

## Current behavior:
 In memory records are dropped when a call is done to self.invalidate_cache
## Expected behavior:
In memory records are preserved when a call is done to self.invalidate_cache


There are lot of places where the method `invalidate_cache` is called and the silent removal of the in memory records from all environments has unpredictable effects on fields modified by a computed method or an onchange or even related fields .... Moreover since all caches are invalidated each time you create / write / unlink  (https://github.com/odoo/odoo/blob/10.0/addons/mail/models/mail_followers.py#L111) an instance of a model that inherits from 'mail.thread', the performances of the server are severely penalized.

OPW703903

max_recipients = 50
        chunks = [email_pids[x:x + max_recipients] for x in xrange(0, len(email_pids), max_recipients)]
        email_ids = []
        for chunk in chunks:
            if message.model and message.res_id and self.pool.get(message.model) and hasattr(self.pool[message.model], 'message_get_recipient_values'):
                recipient_values = self.pool[message.model].message_get_recipient_values(cr, uid, message.res_id, notif_message=message, recipient_ids=chunk, context=context)
            else:
                recipient_values = self.pool['mail.thread'].message_get_recipient_values(cr, uid, message.res_id, notif_message=message, recipient_ids=chunk, context=context)
            mail_values = {
                'mail_message_id': message.id,
                'auto_delete': (context or {}).get('mail_auto_delete', True),
                'mail_server_id': (context or {}).get('mail_server_id', False),
                'body_html': body_html,
                'references': references,
            }
            mail_values.update(custom_values)
            mail_values.update(recipient_values)
            email_ids.append(self.pool.get('mail.mail').create(cr, uid, mail_values, context=context))
        
        
        
        
        
        if force_send and len(chunks) < 2 and \
               (not self.pool._init or
                getattr(threading.currentThread(), 'testing', False)):
            self.pool.get('mail.mail').send(cr, uid, email_ids, context=context)
        return True
    def _notify(self, cr, uid, message_id, partners_to_notify=None, context=None,