maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxx>]

Hi, Aleksey!

On Apr 06, Aleksey Midenkov wrote:
> > > But, since we need to specify implicit system fields we cannot
> > > avoid adding one more session variable. In my current iteration I
> > > made @@force_fields_visible which is more straightforward in what
> > > it does:
> >
> > I'm sorry, I don't understand.
> >
> > First, visibility is pretty much unrelated concept.
> > row_start/row_end can be visible or invisible, and they can be
> > writable or not writable - those are orthogonal concepts.
> 
> To be able to specify them in INSERT command they must be at least
> user-invisible. System-invisible fields are ignored.

Sure, that's what @@system_versioning_insert_history would do.

> > And second, the name is wrong, there are no "fields" row_start and
> > row_end unless the user creates then explicitly. They are pieces of
> > metadata that every row has, something that Oracle, for example,
> > calls "pseudocolumns". Something like
> > @@system_versioning_row_start_row_end_visible would be more correct,
> > but ugly. In fact, I'd say that @@system_versioning_insert_history
> > was the best one.
> 
> I think you are complicating things where complication is not needed.
> Pseudo- or not they are fields.

No, this is internal implementation detail that can change and it should
not leak into the UI. Like, sql_select.cc has a function called
sub_select(), but we never tell users that what it does is "subselect",
not in the documentation, not in error messages, never. Because it
doesn't (it performs one step in a nested-loop join).

The fact that some internal enum value is named INVISIBLE_SYSTEM
is not something that should affect the user visible behavior.

> Besides, the variable is not about system versioning. It can make any
> system-invisible fields visible.

Which is incorrect. ROWNUM (MDEV-24089) is a pseudocolumn, and it cannot
be "visible" in the sense of @force_fields_visible. We don't support
ROWID, but if we would — it cannot be visible in the sense of
@force_fields_visible either. Basically this variable can only apply to
row_start/row_end pseudocolumns, despite its generic name.

Regards,
Sergei
VP of MariaDB Server Engineering
and security@xxxxxxxxxxx