On Sat, Jan 15, 2005 at 05:11:16PM +0100, Bo Lorentsen wrote: > Alvaro Herrera wrote: > >Most system catalogs use OIDs as primary keys. So they cannot just > >disappear. But on user tables, there's not a lot of use for them IMHO. > > > Ok, I think it is about time it is stated more clearly in the documentation. But where in the documentation did you see anything saying that they were unique? I imagine you just inferred that from somewhere. I'm not sure where the documentation should be changed since nowhere actually recommends them in any way. > >There's no internal row id on Postgres; having one would mean more > >storage requirements. If you want one, you know where to get it ... if > >not, you may as well save the space. > > > So, how does a index relate to a row ? There have to be some way of > addressing a row ? Using the CTID, which locates the physical tuple as (block,num). When you update a tuple, or vacuum moves it its CTID will change, so it's not terribly useful from a user's point of view. Hope this helps, -- Martijn van Oosterhout <kleptog@xxxxxxxxx> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
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