Is it acceptable to export and reimport smaller files? Are they images? Are you on Windows or Linux? What version of OpenERP are you running? Have you looked in ~/.local directory of your OpenERP installation?

I a m using openerp 7 on ubuntu 12.04 . I want to write a python script where user add image despite of whatever the size of image is , when user add image the size automatically gets reduce and get stored in database. is this possible?

I know of no automatic function for that. It'd require a special development. Not difficult, but not free either. Sometimes just going for a better performing hosting/server makes the most sense. What is the reason? Slow connection? Small disk?