maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxx>]

Hi, Nikita!

On Feb 08, Nikita Malyavin wrote:
> On Fri, Feb 8, 2019 at 2:18 AM Sergei Golubchik <serg@xxxxxxxxxxx> wrote:
> > I thought you've wanted it a CHECK constraint. You've quoted the
> > standard proving your point of view.
> 
> I've also quoted that it's name shouldn't match any existing
> constraint name:)

yes, we have this issue for all auto-generated names, and the usual
workaround is to append _1, _2, etc until there's a free name.

> > > > diff --git a/sql/table.h b/sql/table.h
> > > > > --- a/sql/table.h
> > > > > +++ b/sql/table.h
> > > > > @@ -1730,6 +1747,9 @@ class IS_table_read_plan;
> > > > >  /** The threshold size a blob field buffer before it is freed */
> > > > >  #define MAX_TDC_BLOB_SIZE 65536
> > > > >
> > > > > +/** number of bytes read by uint2korr and sint2korr */
> > > > > +#define korr2size 2
> > > >
> > > > No, that's silly. It's like #define TWO 2
> > > > Of course korr2size is 2. And korr3size is 3, and korr4size is 4.
> > >
> > > Of course! That's the way to say "This variable was stored as a 2-byte
> > > tuple".
> >
> > I mean, you didn't remove the magic number. It's still 2, and if you'd
> > like to change it to be 3, for example, you'd still need to go and
> > change the code everywhere.
> 
> Oh, so You're really thinking on such refactoring, to change the sizes of
> metainfo types  rapidly? Then that 👇makes sense:

No, I don't. Changing storage format is very heavy and thus very rare
operation.

I was just using it as an example, to show that embedding a magical
number in the name of a constant doesn't make it any less magical or the
code any easier to understand. "Easy to change" is a good rule, even if
you don't actually plan to change :)

> > > That's why I suggested something like
> > > >
> > > >   #define fieldno_size   2
> > > >   #define fieldno_korr   uint2korr
> > > >   #define fieldno_store  int2store
> > > >
> > > Oh no, that'll add 9 new macros! And the number can grow...
> >
> > What do you mean, it's just three new macros, like above. Where's 9?
> 
> 3 for fieldno, 3 for field_name_len, 3 for key_count (WITHOUT OVERLAPS
> commit), and who knows -- I've also planned an flag in FOREIGN KEY support.

sure, they're different entities, there is no inherent rule why they all
should use the same storage width. So yes, 9 macros.

Regards,
Sergei
Chief Architect MariaDB
and security@xxxxxxxxxxx