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
```
""" High-level objects for fields. """
from collections import OrderedDict, defaultdict
from datetime import date, datetime
from functools import partial
from operator import attrgetter
from types import NoneType
import json
import logging
import pytz
import xmlrpclib
import psycopg2
from odoo.sql_db import LazyCursor
from odoo.tools import float_precision, float_repr, float_round, frozendict, \
                       html_sanitize, human_size, pg_varchar, ustr, OrderedSet
from odoo.tools import DEFAULT_SERVER_DATE_FORMAT as DATE_FORMAT
from odoo.tools import DEFAULT_SERVER_DATETIME_FORMAT as DATETIME_FORMAT
from odoo.tools.translate import html_translate, _
DATE_LENGTH = len(date.today().strftime(DATE_FORMAT))
DATETIME_LENGTH = len(datetime.now().strftime(DATETIME_FORMAT))
EMPTY_DICT = frozendict()
RENAMED_ATTRS = [('select', 'index'), ('digits_compute', 'digits')]
_logger = logging.getLogger(__name__)
_schema = logging.getLogger(__name__[:-7] + '.schema')
Default = object()                      
class SpecialValue(object):