maria-developers team mailing list archive

[Alexander Barkov <bar@xxxxxxxxxxx>]

  Hello Sergei,

On 10/25/21 11:03 PM, Sergei Golubchik wrote:
> Hi, Alexander!
>
> On Oct 25, Alexander Barkov wrote:
> > > > MDEV-26732 Assertion `0' failed in Item::val_native
> > > >
> > > > Also fixes MDEV-24619 Wrong result or Assertion `0' in Item::val_native / Type_handler_inet6::Item_val_native_with_conversion
> > >
> > > would be good to have some explanation here, what was wrong, what was
> > > the fix.
> >
> > Right, I suggest this comment:
> >
> >
> >       MDEV-26732 Assertion `0' failed in Item::val_native
> >
> >       Also fixes MDEV-24619 Wrong result or Assertion `0' in
> > Item::val_native / Type_handler_inet6::Item_val_native_with_conversion
> >
> > Type_handler::create_item_copy() created a generic Item_copy_string,
> > which does not implement val_native() - it has a dummy implementation
> > with DBUG_ASSERT(0), which made the server crash.
>
> Why does it call val_native() if Item_copy_string doesn't implement it?

Because I forgot to implement Item_copy_inet6 - I missed the reported
scenario in my original test coverage for INET6.

The default implementation in Item::val_native(), which is called
for Item_copy_string in this scenario, intentionally consists only of 
DBUG_ASSERT.

If it had some working implementation, returning the expected value,
it would hide a performance problem:

Conversion from the string INET6 representation to the binary
INET6 representation would happen per row. This is not desirable.
So the DBUG_ASSERT is a trap to find such places not implementing
fast code paths for the native representation.


> If the item was a string in the first place, that is, if
> Item_copy_string would've been used correctly where it should've been
> used, then val_native() wouldn't be called? What would it use,
> val_str()?

Yes, val_str().

> So why does it use val_native() here, because that
> Item_copy_string uses Type_handler_inet6?

Correct.

> > Fix:
> >
> > - Adding a new class Item_copy_inet6, which implements val_native().
> > - Fixing Type_handler::create_item_copy() to make Item_copy_inet6
> > instead of Item_copy_string.
> Regards,
> Sergei
> VP of MariaDB Server Engineering
> and security@xxxxxxxxxxx