Re: Table AM Interface Enhancements

On Mon, Apr 1, 2024 at 7:36 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Coverity complained about what you did in RelationParseRelOptions
> in c95c25f9a:
>
> *** CID 1595992: Null pointer dereferences (FORWARD_NULL)
> /srv/coverity/git/pgsql-git/postgresql/src/backend/utils/cache/relcache.c: 499 in RelationParseRelOptions()
> 493
> 494 /*
> 495 * Fetch reloptions from tuple; have to use a hardwired descriptor because
> 496 * we might not have any other for pg_class yet (consider executing this
> 497 * code for pg_class itself)
> 498 */
> >>> CID 1595992: Null pointer dereferences (FORWARD_NULL)
> >>> Passing null pointer "tableam" to "extractRelOptions", which dereferences it.
> 499 options = extractRelOptions(tuple, GetPgClassDescriptor(),
> 500 tableam, amoptsfn);
> 501
>
> I see that extractRelOptions only uses the tableam argument for some
> relkinds, and RelationParseRelOptions does set it up for those
> relkinds --- but Coverity's complaint isn't without merit, because
> those two switch statements are looking at *different copies of the
> relkind*, which in theory could be different. This all seems quite
> messy and poorly factored. Can't we do better? Why do we need to
> involve two copies of allegedly the same pg_class tuple, anyhow?

I wasn't registered at Coverity yet. Now I've registered and am
waiting for approval to access the PostgreSQL analysis data.

I wonder why Coverity complains about tableam, but not amoptsfn.
Their usage patterns are very similar.

It appears that relation->rd_rel isn't the full copy of pg_class tuple
(see AllocateRelationDesc). RelationParseRelOptions() is going to
update relation->rd_options, and thus needs a full pg_class tuple to
fetch options out of it. However, it is really unnecessary to access
both tuples at the same time. We can use a full tuple, not
relation->rd_rel, in both cases. See the attached patch.

------
Regards,
Alexander Korotkov