oracle - Adding column with default value

Question

I have a table A (3 columns) in production which is around 10 million records. I wanted to add one more column to that table and also I want to make default value to 1. Is it going to impact production DB performance If add a column with default value 1 or something else. What would be best approach to this to avoid any kind of performance impact on DB? your thoughts are much appreciated!!

Answer 1

In Oracle 11g the process of adding a new column with a default value has been considerably optimized. If a newly added column is specified as NOT NULL, default value for that column is maintained in the data dictionary and it's no longer required for a default value of a column to be stored for all records in a table, so it's no longer required to update each record with a default value. Such an optimization considerably reduces amount of time the table is exclusively locked during the operation.

 alter table <tab_name> add(<col_name> <data_type> default <def_val> not null)

Moreover, column with a default value added that way will not consume space, until you deliberately start to update that column or insert a record with a non default value for that column. So the operation of adding a new column with a default value and not null constraint specified completes pretty quick.

Answer 2

i think that it is better that you create a table as backup table with this syntax:

 create table BackUpTable as SELECT * FROM YourTable;
 alter table BackUpTable add (newColumn number(5,0)default 1);