Re: partitioning and identity column

> On Mon, May 06, 2024 at 06:52:41PM +0530, Ashutosh Bapat wrote:
> On Sun, May 5, 2024 at 1:43 AM Dmitry Dolgov <9erthalion6@gmail.com> wrote:
> > I had a quick look, it covers the issues mentioned above in the thread.
> > Few nitpicks/questions:
> >
> > * I think it makes sense to verify if the ptup is valid. This approach
> >   would fail if the target column of the root partition is marked as
> >   attisdropped.
> >
>
> The column is searched by name which is derived from attno of child
> partition. So it has to exist in the root partition. If it doesn't
> something is seriously wrong. Do you have a reproducer? We may want to add
> Assert(HeapTupleIsValid(ptup)) just in case. But it seems unnecessary to me.

Sure, normally it should work. I don't have any particular situation in
mind, when attisdropped might be set on a root partition, but obviously
setting it manually crashes this path. Consider it mostly as suggestion
for a more defensive implementation "just in case".

> >      Oid
> >     -getIdentitySequence(Oid relid, AttrNumber attnum, bool missing_ok)
> >     +getIdentitySequence(Relation rel, AttrNumber attnum, bool missing_ok)
> >      {
> >
> >     [...]
> >
> >     +           relid = llast_oid(ancestors);
> >     +           ptup = SearchSysCacheAttName(relid, attname);
> >     +           attnum = ((Form_pg_attribute) GETSTRUCT(ptup))->attnum;
> >
> > * getIdentitySequence is used in build_column_default, which in turn
> >   often appears in loops over table attributes. AFAICT it means that the
> >   same root partition search will be repeated multiple times in such
> >   situations if there is more than one identity. I assume the
> >   performance impact of this repetition is negligible?
> >
>
> I thought having multiple identity columns would be rare and hence avoided
> making code complex. Otherwise we have to get root partition somewhere in
> the caller hierarchy separately the logic much farther apart. Usually the
> ancestor entries will be somewhere in the cache

Yeah, agree, it's reasonable to expect that the case with multiple
identity columns will be rare.