Varchar2 to CLOB : Best Options to do it ?

Question

Helllo,
I have a table whcih is 20GB in size and has a Column which is a Varchar2 column.As varchar2 could store upto 4000 bytes of data,we have a requiremnet where the column can have more than 4000 bytes of data and we decided to convert it to a CLOB column.
What are the best and fastest way of doing this?
OPTION 1_
1. First create the temporary table
CREATE TABLE P_C_V_NEW
(TESTID_NUM NUMBER,
DATAPOINT NUMBER,
DATAPOINT_DATE DATE ,
CHANGE_FLAG VARCHAR2(1),
CHANNEL_VALUES CLOB )
2. Insert the data from original to the temporaray table
INSERT INTO P_C_V_NEW (SELECT TESTID_NUM,DATAPOINT, DATAPOINT_DATE, CHANGE_FLAG,CHANNEL_VALUES FROM P_C_V)
3.Rename the temporary table to Original table
RENAME P_C_V_NEW TO PAM_CHANNEL_VALUES
OPTION 2:_
SQL> alter table P_C_V add (NEW_CHANNEL_VALUE clob);
Table altered.
SQL> update P_C_V set NEW_CHANNEL_VALUE = CHANNEL_VALUE;
1 row updated.
SQL> alter table PP_C_V drop column CHANNEL_VALUE;
Table altered.
SQL> alter table P_C_V rename column NEW_CHANNEL_VALUE to CHANNEL_VALUE;
Table altered.
SQL> desc pam_channel_values
Name Null? Type
TESTID_NUM NUMBER
DATAPOINT      NOT NULL NUMBER
DATAPOINT_DATE      NOT NULL DATE
CHANGE_FLAG      NOT NULL CHAR(1)
CHANNEL_VALUES CLOB
OPTION 3
Use DBMS_REDEFINITION ?
This original table contains 11714457 records.
Thanks
GAG

Answer 1

I would prefer somthing as like method1 as
Create table x as select * from old table.
beacuse it would be the fastest way to load the data compare to update of method 2.
Only issue is that the in table x the new constriant and index need to be created if they are presenti on old .
and even if you want to go with method 2 you need to do the update in BULK collect way in plsql
not simple sql like this beacuse you need a big amount of rollback segment spac
update P_C_V set NEW_CHANNEL_VALUE = CHANNEL_VALUE;Cheers
Nawneet