I think i fix the problem.

We are accessing port 8072 as daily operation, and recently i do some heavy load import to odoo via 8069 port, in purpose not to disturb the traffic at 8072. But i think that's what makes it error, until i restart postgres and odoo-server service. Then, i do my heavy load import via 8072, and the problem hasn't occur until today.

EDIT : We switch 8069 port as daily operation as Odoo documentation suggest, but the problem is still occurs, until i did the quick fix to restarting nginx and postgresql by typing :

service postgresql@11-main restart
service nginx restart

"11-main" depends on your postgresql version (EG : version 9 then type 9-main)

To prevent it from happening again, i use crontab to schedule postgres to restart every x hour.

Altela (altelasoftware.com)