Michael Paquier wrote: > 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.
Maybe we need to document this somewhere, particularly now that we have a "table_rewrite" event item. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services