On Fri, Jan 19, 2018 at 11:33:43AM -0500, Tom Lane wrote:
> It means reading the whole table and writing it out in some modified
> form (for instance, with some column transformed into a new datatype).
> It's not "dangerous" in any way ... but if you've got many GB of data in
> the table and you can't afford to have the table locked for a long time,
> then it's something to avoid.
Yeah that can be costly. Note that WAL corresponding to this data needs
to be generated as well.
--
Michael