Alter table/ Add column

Here is my simple question. Why is it that adding a column to a table will generate a lot of redo log info. I thought you just added it and that was that, my senior DBA says that is not the case. Can anyone explain this one to me?

Thanks, MH

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Originally posted by Mr.Hanky
Here is my simple question. Why is it that adding a column to a table will generate a lot of redo log info. I thought you just added it and that was that, my senior DBA says that is not the case. Can anyone explain this one to me?

Thanks, MH

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If i am right, Add a column will not generate a lot of redo log info. But if the column has a default value in it, it is. Because alle rows wil be updated with the default value. First add the column with NULL values, After this update the column with values.