On Wed, Jul 13, 2016 at 03:57:02PM -0500, Kevin Grittner wrote: > On Wed, Jul 13, 2016 at 12:48 PM, Andres Freund <and...@anarazel.de> wrote: > > On 2016-07-13 10:06:52 -0500, Kevin Grittner wrote: > >> On Wed, Jul 13, 2016 at 7:57 AM, Amit Kapila <amit.kapil...@gmail.com> > >> wrote: > >>> On Tue, Jul 12, 2016 at 8:34 PM, Kevin Grittner <kgri...@gmail.com> wrote: > >>>> On Fri, Jul 8, 2016 at 1:52 PM, Andres Freund <and...@anarazel.de> wrote: > >>>> > >>>>> I'm a bit confused, why aren't we simply adding LSN interlock > >>>>> checks for toast? Doesn't look that hard? Seems like a much more > >>>>> natural course of fixing this issue? > >>>> > >>>> I took some time trying to see what you have in mind, and I'm > >>>> really not "getting it". > >>> > >>> Isn't it possible if we initialize lsn and whenTaken in SnapshotToast > >>> when old_snapshot_threshold > 0 and add a check for > >>> HeapTupleSatisfiesToast in TestForOldSnapshot()? > >> > >> With that approach, how will we know *not* to generate an error > >> when reading the chain of tuples for a value we are deleting. Or > >> positioning to modify an index on toast data. Etc., etc. etc. > > > > I'm not following. How is that different in the toast case than in the > > heap case? > > A short answer is that a normal table's heap doesn't go through > systable_getnext_ordered(). That function is used both for cases > where the check should not be made, like toast_delete_datum(), and > cases where it should, like toast_fetch_datum(). > > Since this keeps coming up, I'll produce a patch this way. I'm > skeptical, but maybe it will look better than I think it will. I > should be able to post that by Friday.
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