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
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