I'll tell you why - try to update one column in 100GB worth of row data.
Postgress makes a copy of _every_ row and you need 100GB of extra space on the hard-drive until you commit the transaction. Now extrapolate to a 1TB table that needs updating.
Oracle has a way of doing this w/o copying the entire row.
Postgress makes a copy of _every_ row and you need 100GB of extra space on the hard-drive until you commit the transaction. Now extrapolate to a 1TB table that needs updating.
Oracle has a way of doing this w/o copying the entire row.