Dear Eirik Hanssen
If you are running your OJS on a shared server hosting, you shall not have control over php.ini file setting. OJS enforces dB based session log as mentioned in DB Error: Duplicate entry 'xxxxxx' for key 'sessions_pkey' - #18 by asmecher. For further insight see this post DB Error: Duplicate entry 'xxxxxx' for key 'sessions_pkey' - #13 by Umadhar. You can output phpinfo() and see the settings. you can override the php.ini settings by using user.ini or .htaccess file. In user.ini file i have commented out the below parameters so that OJS overrides the php.ini setting for logging sessions.
;session.save_handler
;session.save_path =
Hope it answers your question.