Re: pgsql: Teach verify_heapam() to validate update chains within a page.

Hi,

On 2023-03-22 15:33:15 -0400, Andrew Dunstan wrote:
> On 2023-03-22 We 09:17, Robert Haas wrote:
> > Teach verify_heapam() to validate update chains within a page.
> > 
> > Prior to this commit, we only consider each tuple or line pointer
> > on the page in isolation, but now we can do some validation of a line
> > pointer against its successor. For example, a redirect line pointer
> > shouldn't point to another redirect line pointer, and if a tuple
> > is HOT-updated, the result should be a heap-only tuple.
> > 
> > Himanshu Upadhyaya and Robert Haas, reviewed by Aleksander Alekseev,
> > Andres Freund, and Peter Geoghegan.
> 
> 
> This has apparently broken one case in the buildfarm, which now fails an
> upgrade from REL9_2_STABLE because we run amcheck after the upgrade:
> 
> 
> heap table "regression.public.xacttest", block 0, offset 1:
>     non-heap-only update produced a heap-only tuple at offset 18
> heap table "regression.public.xacttest", block 0, offset 2:
>     non-heap-only update produced a heap-only tuple at offset 19
> heap table "regression.public.xacttest", block 0, offset 4:
>     non-heap-only update produced a heap-only tuple at offset 20
> heap table "regression.public.xacttest", block 0, offset 5:
>     non-heap-only update produced a heap-only tuple at offset 21
> heap table "regression.public.wslot", block 0, offset 89:
>     non-heap-only update produced a heap-only tuple at offset 95
> heap table "regression.public.pslot", block 0, offset 95:
>     non-heap-only update produced a heap-only tuple at offset 100
> heap table "regression.public.pslot", block 0, offset 96:
>     non-heap-only update produced a heap-only tuple at offset 101
> 
> 
> I don't know if this is a bug in this commit or if the REL9_2_STABLE repo is
> really broken.

FWIW, I get errors on a bunch of catalog tables, on HEAD, if I run the
regression tests and then run amcheck.

heap table "ecpg1_regression.pg_catalog.pg_class", block 7, offset 16:
    non-heap-only update produced a heap-only tuple at offset 19
heap table "ecpg1_regression.pg_catalog.pg_class", block 13, offset 49:
    non-heap-only update produced a heap-only tuple at offset 52
heap table "ecpg1_regression.pg_catalog.pg_class", block 13, offset 53:
...
heap table "regression_pg_surgery.pg_catalog.pg_class", block 0, offset 4:
    non-heap-only update produced a heap-only tuple at offset 5
heap table "regression_pg_surgery.pg_catalog.pg_class", block 0, offset 5:
    non-heap-only update produced a heap-only tuple at offset 6


So either this very quickly bagged the first bugs, or there's something wrong
with the checks.

Greetings,

Andres Freund