Re: Table AM Interface Enhancements

On Mon, Apr 1, 2024 at 7:36 PM Tom Lane <tgl@sss.pgh.pa.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