maria-developers team mailing list archive

[Aleksey Midenkov <midenok@xxxxxxxxx>]

Hi Sergei!

On Sun, Oct 17, 2021 at 4:55 PM Sergei Golubchik <serg@xxxxxxxxxxx> wrote:
>
> Hi, Aleksey!
>
> On Oct 17, Aleksey Midenkov wrote:
> > commit 8a84f5a40c1
> > Author: Aleksey Midenkov <midenok@xxxxxxxxx>
> > Date:   Thu May 27 17:00:14 2021 +0300
> >
> >     MDEV-24176 Preparations
> >
> >     1. moved fix_vcol_exprs() call to open_table()
> >
> >     mysql_alter_table() doesn't do lock_tables() so it cannot win from
> >     fix_vcol_exprs() from there. Tests affected: main.default_session
>
> This is likely wrong, but the old code was wrong too. Neither open_table
> nor lock_tables is called under LOCK TABLES, but the session
> environment can change, I suspect.

Why, open_table() is called under LOCK TABLES. Please see there `if
(best_table)` and a jump to reset where vcol_fix_exprs() is called.
Added test case for LOCK TABLES.

>
> >
> >     2. cleanup_excluding_fields_processor removed.
> >
> >     That was just a quick hack to exclude wrongly working Item_field from
> >     processing. Now it works due to correct execution environment (see
> >     next commit). Related to MDEV-10355
>
> does it work now, in that commit, or only after the next commit?

It is for the next commit actually. Moved that there.


> what exactly do you mean by correct execution environment?

This is what Vcol_expr_context does.

>
> >
> >     3. Vanilla cleanups and comments.
> >
> > diff --git a/sql/item.h b/sql/item.h
> > index cc1914a7ad4..7b7fe04f0b2 100644
> > --- a/sql/item.h
> > +++ b/sql/item.h
> > @@ -2586,6 +2585,12 @@ class Item_ident :public Item_result_field
> >    const char *db_name;
> >    const char *table_name;
> >    const char *field_name;
> > +  /*
> > +     NOTE: came from TABLE::alias_name_used and this is only a hint! It works
> > +     only in need_correct_ident() condition. On other cases it is FALSE even if
> > +     table_name is alias! It cannot be TRUE in these cases, lots of spaghetti
> > +     logic depends on that.
>
> could you elaborate on that?

See in next commit check_vcol_func_processor(). I could use `if
(alias_name_used)` instead of `if (table_name)` if alias_name_used
were updated correctly. But it is used only for limited subset of
cases (so is not always true when alias is specified). Improving
alias_name_used caused me some failures (in find_field_in_tables()
AFAIR), so I had to mark VCOL_TABLE_ALIAS for every existing
Item_ident::table_name. That triggers redundant expr update for some
cases.

>
> > +  */
> >    bool alias_name_used; /* true if item was resolved against alias */
> >    /*
> >      Cached value of index for this field in table->field array, used by prep.
>
> Regards,
> Sergei
> VP of MariaDB Server Engineering
> and security@xxxxxxxxxxx



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