Recently we have faced the same problem. We're trying to create table with dynamic colums, after that while updating the data it was shown that row size too big error. After as per our DBA lead suggestion, we done some chsnges like "there is one date column its taking lenght high because of it is timestamp format, thats why we cast that column with date data type". By this lenght became 10, obviously space released problem solved. But this same cause not for all the time for that error. So first check your data if there is any unnecessary thing avoid it. Its my first experience for this error.
I've also read about TOAST-able and so on and I haven't messed with storage properties. The data into that columns aren't big numbers (maybe having many decimal counts)
