`--db_maxconn`¶

Here is definition from odoo/tools/config.py

group.add_option("--db_maxconn", dest="db_maxconn", type='int', my_default=64,
                 help="specify the the maximum number of physical connections to posgresql")

More accurate explanantion of this option is as following:

db_maxconn – specify the the maximum number of physical connections to posgresql per odoo process, but for all databases

How much process odoo runs?

longpolling – no more than 1 process
workers
max_cron_threads

What it means practically?

If you have deployment with big number of databases or simultaneous users you may face following error:

2017-09-11 14:01:14,876 8676 ERROR ? odoo.service.server: Worker (8676) Exception occured, exiting...
Traceback (most recent call last):
  File "/opt/odoo/10/odoo/service/server.py", line 721, in run
    self.process_work()
  File "/opt/odoo/10/odoo/service/server.py", line 791, in process_work
    db_names = self._db_list()
  File "/opt/odoo/10/odoo/service/server.py", line 784, in _db_list
    db_names = odoo.service.db.list_dbs(True)
  File "/opt/odoo/10/odoo/service/db.py", line 325, in list_dbs
    with closing(db.cursor()) as cr:
  File "/opt/odoo/10/odoo/sql_db.py", line 622, in cursor
    return Cursor(self.__pool, self.dbname, self.dsn, serialized=serialized)
  File "/opt/odoo/10/odoo/sql_db.py", line 164, in __init__
    self._cnx = pool.borrow(dsn)
  File "/opt/odoo/10/odoo/sql_db.py", line 505, in _locked
    return fun(self, *args, **kwargs)
  File "/opt/odoo/10/odoo/sql_db.py", line 573, in borrow
    **connection_info)
  File "/usr/local/lib/python2.7/dist-packages/psycopg2/__init__.py", line 164, in connect
    conn = _connect(dsn, connection_factory=connection_factory, async=async)
OperationalError: FATAL:  remaining connection slots are reserved for non-replication superuser connections

To resolve it you need configure following parameters:

In odoo
- db_maxconn
- workers
- max_cron_threads
In posgresql
- max_connections

Those parameters must satisfy following condition:

(1 + workers + max_cron_threads) * db_maxconn < max_connections

For example, if you have following values:

workers = 1 (minimal value to make longpolling work)
max_cron_threads = 2 (default)
db_maxconn = 64 (default)
max_connections = 100 (default)

then (1 + 1 + 2) * 64 = 256 > 100, i.e. the condition is not satisfied and such deployment may face the error described above.

--db_maxconn¶

`--db_maxconn`¶