Logical log size

I looked all around and couldn't find any info, so, here goes . . . How much logical log space is used on an update? I will be updating two columns (smallint) of each record on various tables in my system, along the lines of . . . update table_name set upd_a = new_value_a, upd_b = new_value_b where upd_a = old_value_a and upd_b = old_value_b The two ideas I have now would be to : 1. select subset of table begin work update subset of table commit work repeat until no more subsets. or 2. select all rows from table begin work update commit work select rows from next table. The problem I have is one of granularity. I'd like to be able to update an entire table on a transaction, but I'd like to plan ahead to see if it is even possible. Is there any way to determine how much logical log space a two-column update would take?? TIA John Carlson Informix DBA WH Smith, Inc. Last seen: Trying to get all projects caught up after the Conference.