On large recordsets I got some severe performance issues while browsing through an inherits relation.
For example I have a batch process exporting a csv file with products variants:

I have to export 50.000 products.

If I do :
`variant.categ_id` It takes a very long time to get the result.

If I do:
`variant.product_tmpl_id.categ_id` The result is immediate

The problem is that the global perfomance of the application is impacted by this problem.

For example my POS takes more than 15 minutes to load. Because I have 26.000 products and the compute price method uses a lot browsing through the inherits such like `product.cated_id`, `product.uom_id` and they all takes a huge time to compute.

Same issue in this case.

If I do :
`variant.price` It takes a very long time to get the result.

If I do:
`variant.product_tmpl_id.price` The result is immediate

Could you help me ?


Simple way to reproduce:

1/ Create a new database and install sale module
2/ Launch following script through odoo shell :

```python
# -*- coding: utf-8 -*-
import logging

_logger = logging.getLogger(__name__)
self = self  # noqa

nb_product = 50000

i = 0
while i < nb_product:
    prod = self.env['product.template'].create({'name': 'product_%s' % i})
    i += 1
    if i % 1000 == 0:
        self.env.cr.commit()
        _logger.info("%s Products Created" % i)
```

2/ Launch following script through odoo shell :
```python
# -*- coding: utf-8 -*-
import logging

_logger = logging.getLogger(__name__)
self = self  # noqa


products = self.env['product.product'].search([])

for product in products:
    # Immediate response
    _logger.info('Category Template %s' % product.product_tmpl_id.categ_id)
    # Lagging response
    _logger.info('Category Variant %s' % product.categ_id) 
    break
```
"""  exists() -> records
        Returns the subset of records in ``self`` that exist, and marks deleted
        records as such in cache. It can be used as a test on records::
            if record.exists():
                ...
        By convention, new records are returned as existing.
        """
        ids, new_ids = [], []
        for i in self._ids:
            (ids if isinstance(i, (int, long)) else new_ids).append(i)
        if not ids:
            return self
        query = """SELECT id FROM "%s" WHERE id IN %%s""" % self._table
        self._cr.execute(query, [tuple(ids)])
        ids = [r[0] for r in self._cr.fetchall()]
        existing = self.browse(ids + new_ids)
        if len(existing) < len(self):
            
            exc = MissingError(_("Record does not exist or has been deleted."))
            (self - existing)._cache.update(FailedValue(exc))
        return existing
    @api.multi
    def _check_recursion(self, parent=None):