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/models.py
""" Check if the given name is a valid model name.
        The _name attribute in osv and osv_memory object is subject to
        some restrictions. This function returns True or False whether
        the given name is allowed or not.
        TODO: this is an approximation. The goal in this approximation
        is to disallow uppercase characters (in some places, we quote
        table/column names and in other not, which leads to this kind
        of errors:
            psycopg2.ProgrammingError: relation "xxx" does not exist).
        The same restriction should apply to both osv and osv_memory
        objects for consistency.
    """
    if regex_object_name.match(name) is None:
        return False
    return True
def raise_on_invalid_object_name(name):
    if not check_object_name(name):
        msg = "The _name attribute %s is not valid." % name
        raise ValueError(msg)
def check_pg_name(name):
    """ Check whether the given name is a valid PostgreSQL identifier name. """
    if not regex_pg_name.match(name):
        raise ValidationError("Invalid characters in table name %r" % name)
    if len(name) > 63:
        raise ValidationError("Table name %r is too long" % name)
regex_private = re.compile(r'^(_.*|init)$')
def check_method_name(name):