Re: BUG #17245: Index corruption involving deduplicated entries

On 2021-10-30 15:11:18 -0700, Peter Geoghegan wrote:
> On Sat, Oct 30, 2021 at 1:42 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > I think it probably is worth adding an error check someplace that verifies
> > that problems of this kind will be detected with, uh, less effort.
>
> The draft fix is something I wanted to get out quickly to signal that
> the bug is definitely going to be fixed soon. I'll need to carefully
> think about this some more on Monday, to make sure that it becomes
> much harder to break in roughly the same way once again.

Makes sense.

> > ISTM that at least a basic version of this is worth doing as a check throwing
> > an ERROR, rather than an assertion. It's hard to believe this'd be a
> > significant portion of the cost of heap_index_delete_tuples(), and I think it
> > would help catch problems a lot earlier.
>
> I like the idea of doing that, but only on master.

Hm. I wonder if it's not actually good to do something like it in 14, given
that we know of a path to have corrupted indexes out there.

> Separately, we should add an assertion that catches cases where a TID
> in the index points to an LP_REDIRECT line pointer, which does not
> point to a heap tuple with storage.

Is it actually guaranteed that that's impossible to happen and wasn't ever
possible? It's not obvious to me that a LP_REDIRECT pointing to an LP_DEAD
tuple would be a real problem.

Greetings,

Andres Freund