On Wed, 18 Dec 2019 at 14:06, Tom Lane <t...@sss.pgh.pa.us> wrote: > Simon Riggs <si...@2ndquadrant.com> writes: > > I present a patch to allow READ UNCOMMITTED that is simple, useful and > > efficient. > > Won't this break entirely the moment you try to read a tuple containing > toasted-out-of-line values? There's no guarantee that the toast-table > entries haven't been vacuumed away. > > I suspect it can also be broken by cases involving, eg, dropped columns. > There are a lot of assumptions in the system that no one will ever try > to read dead tuples. >
This was my first concern when I thought about it, but I realised that by taking a snapshot and then calculating xmin normally, this problem would go away. So this won't happen with the proposed patch. > The fact that you can construct a use-case in which it's good for > something doesn't make it safe in general :-( > I agree that safety is a concern, but I don't see any safety issues in the patch as proposed. -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Solutions for the Enterprise
