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
```
odoo/fields.py
super(MetaField, cls).__init__(name, bases, attrs)
        if cls.type and cls.type not in MetaField.by_type:
            MetaField.by_type[cls.type] = cls
        
        cls.related_attrs = []
        cls.description_attrs = []
        for attr in dir(cls):
            if attr.startswith('_related_'):
                cls.related_attrs.append((attr[9:], attr))
            elif attr.startswith('_description_'):
                cls.description_attrs.append((attr[13:], attr))
class Field(object):
    """ The field descriptor contains the field definition, and manages accesses
        and assignments of the corresponding field on records. The following
        attributes may be provided when instanciating a field:
        :param string: the label of the field seen by users (string); if not
            set, the ORM takes the field name in the class (capitalized).
        :param help: the tooltip of the field seen by users (string)
        :param readonly: whether the field is readonly (boolean, by default ``False``)
        :param required: whether the value of the field is required (boolean, by
            default ``False``)
        :param index: whether the field is indexed in database (boolean, by
            default ``False``)
        :param default: the default value for the field; this is either a static