> On Jan 7, 2020, at 12:15 PM, Alan Hodgson <ahodgson@xxxxxxxxxxxxxxx> wrote: > > On Tue, 2020-01-07 at 11:58 -0900, Israel Brewster wrote: >>> >> Really? Why? With the update I am only changing data - I’m not adding >> any additional data, so the total size should stay the same, right? >> I’m obviously missing something… :-) >> > > PostgreSQL keeps the old row until it gets vacuumed, as it needs to be > visible to other transactions. Not only that, but every index record > gets updated to point to the location of the new data row too (excluding > HOT), and those old index blocks also need to get vacuumed. And none of > those rows can get removed until your update finishes. > > I know this isn't universally true with HOT and fillfactor etc. but with > an update this big I think it's safe to say most of the space will get > doubled. > > Plus you'll get a ton of write-ahead logs. Gotcha. Batches with VACUUM it is! Thanks for the info. --- Israel Brewster Software Engineer Alaska Volcano Observatory Geophysical Institute - UAF 2156 Koyukuk Drive Fairbanks AK 99775-7320 Work: 907-474-5172 cell: 907-328-9145 > > >
