[IMP] base: reduce new DB size by ordering columns

Postgres is aligning columns to 4 or 8 bytes, depending on their type.
So, consecutive fixed-length columns of differing size will be padded
with empty bytes due to the alignment requirements.

Before this patch, columns where created in their definition order. Now,
they are ordered based on their size, in order to minimize the padding.

As an example, before each row uses 36 bytes (+24b header):

       attname   |  typname  | typlen
    -------------+-----------+--------
     id          | int4      |      4
     create_uid  | int4      |      4
     create_date | timestamp |      8
     write_uid   | int4      |      4    -> 4 bytes padding
     write_date  | timestamp |      8
     active      | bool      |      1    -> 3 bytes padding

After each row uses 32 bytes (4 bytes saved per row):

       attname   |  typname  | typlen
    -------------+-----------+--------
     id          | int4      |      4
     create_uid  | int4      |      4
     write_uid   | int4      |      4
     active      | bool      |      1    -> 3 bytes padding
     create_date | timestamp |      8
     write_date  | timestamp |      8

This saving scheme applies to all rows in all tables. We save between 4
and 8 bytes per row just on the usual create_uid, create_date,
write_uid, write_date.

closes odoo/odoo#87896

Signed-off-by: Raphael Collet <rco@odoo.com>

odoo/tools/sql.py

@@ -6,6 +6,7 @@
 import logging
 import psycopg2
 import odoo.sql_db
+from collections import defaultdict
 from contextlib import closing
 
 _schema = logging.getLogger('odoo.schema')
@@ -50,6 +51,17 @@ def table_kind(cr, tablename):
     cr.execute(query, (tablename,))
     return cr.fetchone()[0] if cr.rowcount else None
 
+# prescribed column order by type size: 4 bytes, 1 byte, 8 bytes, variable size
+# (values have been chosen to minimize padding in rows; unknown column types
+# are considered variable size and put last)
+SQL_ORDER_BY_TYPE = defaultdict(lambda: 6, {
+    'int4': 1,        # 4 bytes
+    'date': 2,        # 4 bytes
+    'bool': 3,        # 1 byte
+    'float8': 4,      # 8 bytes
+    'timestamp': 5,   # 8 bytes
+})
+
 def create_model_table(cr, tablename, comment=None, columns=()):
     """ Create the table for a model. """
     colspecs = ['id SERIAL NOT NULL'] + [