Re: Alter the column data type of the large data volume table.

On Thu, Dec 3, 2020 at 10:18 AM Rich Shepard <rshepard(at)appl-ecosys(dot)com>
wrote:

> On Thu, 3 Dec 2020, Michael Lewis wrote:
>
> > On Wed, Dec 2, 2020 at 11:53 PM charles meng <xlyybz(at)gmail(dot)com> wrote:
>
> >> I have a table with 1.6 billion records. The data type of the primary
> key
> >> column is incorrectly used as integer. I need to replace the type of the
> >> column with bigint. Is there any ideas for this?
>
> > You can add a new column with NO default value and null as default and
> have
> > it be very fast. Then you can gradually update rows in batches (if on
> > PG11+, perhaps use do script with a loop to commit after X rows) to set
> the
> > new column the same as the primary key. Lastly, in a transaction, update
> > any new rows where the bigint column is null, and change which column is
> > the primary key & drop the old one. This should keep each transaction
> > reasonably sized to not hold up other processes.
>
> Tell me, please, why
>
> ALTER TABLE <tablename> ALTER COLUMN <columnname> SET DATA TYPE BIGINT
>
> will not do the job?
>
> I've found some varchar columns in a couple of tables too small and used
> the
> above to increase their size. Worked perfectly.
>
> Regards,
>
> Rich
>

Afaik, it will require an access exclusive lock for the entire time it
takes to re-write the 1.6 billion rows and update all indexes. That sort of
lock out time doesn't seem workable in many production systems.