Table modification transaction size problem

Hello, I have a esql-c program that is going to alter a table. This is Online database with transactions I need to calculate if this alter will hang due to the size of the transaction being to big. I would assume I need to calucate how big the transaction would be and then calulate how big of a transaction my online system can handle. Has anyone ever done this??? Any sugestions?? Thanks Randy Paries rtparies@ingr.com