Re: [Maria-developers] MDEV-17399: JSON_TABLE: final input

[Alexey Botchkov]

The Json_table_nested_path lives only inside the Table_function_json_table
and that last one
is the only class that manipulates the Json_table_nested_path internals.
Using methods
in your version, but it's the only class using these methods anyway.
So to me it's seems more honest to declare classes as friends so we
explicitly allow access to
the internals to that one class and disallow to everyone else.

But yes, it's rather the matter of taste.

Best regards.
HF


On Fri, Mar 12, 2021 at 2:33 AM Sergey Petrunia  wrote:

> On Sat, Mar 06, 2021 at 01:13:53AM +0400, Alexey Botchkov wrote:
> > Hi, Sergei!
> >
> > I pushed the patch to the feature branch for you to take a look.
> > The patch you proposed
> > http://lists.askmonty.org/pipermail/commits/2021-March/014492.html
> >  I liked and adapted with one exception. The nested paths list is built
> > using the **last_sibling_hook
> > instead of *cur_last_sibling. That seems to me nicer and doesn't produce
> > that many repeating lines
> > in the code.
> >
>
> On the other hand, use of "last_sibling_hook" makes
> Table_function_json_table to
> be aware about the internals of Json_table_nested_path (you had to make it
> a
> friend class).
>
> And the price to pay for complete isolation was the if-else in
> start_nested_path(), with two lines in either branch.
> So I would still say that the suggested solution was cleaner.
>
> I don't consider this to be a showstopper issue, though.
>
> BR
>  Sergei
> --
> Sergei Petrunia, Software Developer
> MariaDB Corporation | Skype: sergefp | Blog: http://petrunia.net
>
>
>
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Re: [Maria-developers] MDEV-17399: JSON_TABLE: Incorrect code with table elimination

[Alexey Botchkov]

I've rewritten it using the json->select_lex->leaf_tables as you suggested.
So the JSON_TABLE is calculated properly and all the dependencies seem to
be marked.
Still your testcase query fails the same way, so needs some more
investigation. To me it
looks more like optimizer issue than the JSON_TABLE-s.

Best regards.
HF


On Fri, Mar 12, 2021 at 2:21 AM Sergey Petrunia  wrote:

> Hi Alexey,
>
> > diff --git a/sql/opt_table_elimination.cc b/sql/opt_table_elimination.cc
> > index 3958797ec44..f2497d524ec 100644
> > --- a/sql/opt_table_elimination.cc
> > +++ b/sql/opt_table_elimination.cc
> > @@ -637,6 +637,16 @@ void eliminate_tables(JOIN *join)
> >List_iterator it(join->fields_list);
> >while ((item= it++))
> >  used_tables |= item->used_tables();
> > +
> > +  {
> > +List_iterator it(*join->join_list);
> > +TABLE_LIST *tbl;
> > +while ((tbl= it++))
> > +{
> > +  if (tbl->table_function)
> > +used_tables|= tbl->table_function->used_tables();
> > +}
> > +  }
> >
>
> This only walks the tables that are "at the top level" of the join. if a
> JSON_TABLE(...) is inside a nested outer join, it will not be found.
>
> Please walk select_lex->leaf_tables instead. Please add the testcase (I
> provide
> one below).
>
> Please also add a comment, clarifying what is being done, something like:
>
>   Table function JSON_TABLE() can have references to other tables. Do not
>   eliminate the tables that JSON_TABLE() refers to. Note: the JSON_TABLE
> itself
>   cannot be eliminated as it doesn't have unique keys.
>
> == Testcase ==
>
>
> create table t20 (a int not null);
> create table t21 (a int not null primary key, js varchar(100));
>
> insert into t20 select seq from seq_1_to_100;
> insert into t21 select a, '{"a":100}' from t20;
>
> create table t31(a int);
> create table t32(b int);
> insert into t31 values (1);
> insert into t32 values (1);
>
> explain
> select
>   t20.a, jt1.ab
> from
>   t20
>   left join t21 on t20.a=t21.a
>   join
>   (t31 left join (t32 join JSON_TABLE(t21.js,'$' COLUMNS (ab INT PATH
> '$.a')) AS jt1) on t31.a<3);
>
>
> BR
>  Sergei
> --
> Sergei Petrunia, Software Developer
> MariaDB Corporation | Skype: sergefp | Blog: http://petrunia.net
>
>
>
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