Re: [Maria-developers] MDEV-17399: JSON_TABLE, commit 85757ecbef44484270e385a8d52998c67f72d11a
Ok, fixed that as you said.
See the last commit to the bb-10.6-mdev17399-hf for details
Best regards.
HF
On Tue, Feb 23, 2021 at 3:57 PM Sergey Petrunia wrote:
> On Mon, Feb 22, 2021 at 09:59:54PM +0300, Sergey Petrunia wrote:
> > == On table dependencies: table elimination ==
> >
> > create table t20 (a int not null);
> > create table t21 (a int not null primary key, js varchar(100));
> >
> > insert into t20 values (1),(2);
> > insert into t21 values (1, '{"a":100}');
> >
> > explain
> > select
> > t20.a, jt1.ab
> > from
> > t20
> > left join t21 on t20.a=t21.a
> > join JSON_TABLE(t21.js,'$' COLUMNS (ab INT PATH '$.a')) AS jt1;
> >
> >
> +--+-+---+--+---+--+-+--+--++
> > | id | select_type | table | type | possible_keys | key | key_len |
> ref | rows | Extra |
> >
> +--+-+---+--+---+--+-+--+--++
> > |1 | SIMPLE | t20 | ALL | NULL | NULL | NULL|
> NULL | 2||
> > |1 | SIMPLE | jt1 | ALL | NULL | NULL | NULL|
> NULL | 40 | Table function: json_table |
> >
> +--+-+---+--+---+--+-+--+--++
> >
> > Here we can see an apparently invalid query plan: table t21 was
> eleminated
> > even if JSON_TABLE uses it.
>
> We can do with a simple rule: "do not eliminate tables that are used as
> argument for any table function".
>
> I think this should be achieved as follows: in eliminate_tables(), look
> at the code that collects a bitmap of tables used in the select list (to
> prevent them from being eliminated).
>
> /* Add tables referred to from the select list */
> List_iterator it(join->fields_list);
> while ((item= it++))
> used_tables |= item->used_tables();
>
> Right below this, add a loop which does the same for table functions.
>
>
> 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, commit 85757ecbef44484270e385a8d52998c67f72d11a
On Mon, Feb 22, 2021 at 09:59:54PM +0300, Sergey Petrunia wrote:
> == On table dependencies: table elimination ==
>
> create table t20 (a int not null);
> create table t21 (a int not null primary key, js varchar(100));
>
> insert into t20 values (1),(2);
> insert into t21 values (1, '{"a":100}');
>
> explain
> select
> t20.a, jt1.ab
> from
> t20
> left join t21 on t20.a=t21.a
> join JSON_TABLE(t21.js,'$' COLUMNS (ab INT PATH '$.a')) AS jt1;
>
> +--+-+---+--+---+--+-+--+--++
> | id | select_type | table | type | possible_keys | key | key_len | ref |
> rows | Extra |
> +--+-+---+--+---+--+-+--+--++
> |1 | SIMPLE | t20 | ALL | NULL | NULL | NULL| NULL |
> 2||
> |1 | SIMPLE | jt1 | ALL | NULL | NULL | NULL| NULL |
> 40 | Table function: json_table |
> +--+-+---+--+---+--+-+--+--++
>
> Here we can see an apparently invalid query plan: table t21 was eleminated
> even if JSON_TABLE uses it.
We can do with a simple rule: "do not eliminate tables that are used as
argument for any table function".
I think this should be achieved as follows: in eliminate_tables(), look
at the code that collects a bitmap of tables used in the select list (to
prevent them from being eliminated).
/* Add tables referred to from the select list */
List_iterator it(join->fields_list);
while ((item= it++))
used_tables |= item->used_tables();
Right below this, add a loop which does the same for table functions.
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, commit 85757ecbef44484270e385a8d52998c67f72d11a
On Mon, Feb 22, 2021 at 09:59:54PM +0300, Sergey Petrunia wrote:
> == On table dependencies: regular subqueries ==
>
> But it doesn't work for regular subqueries either (and this is unexpected):
>
> insert into t21 values (3, '{"a":300}');
>
> explain
> select
> a,
> (select jt1.ab
>from JSON_TABLE(t21.js,'$' COLUMNS (ab INT PATH '$.a')) as jt1
> )
> from t21;
>
> +--+-+---+--+---+--+-+--+--++
> | id | select_type | table | type | possible_keys | key | key_len | ref |
> rows | Extra |
> +--+-+---+--+---+--+-+--+--++
> |1 | PRIMARY | t21 | ALL | NULL | NULL | NULL| NULL |
> 2||
> |2 | SUBQUERY| jt1 | ALL | NULL | NULL | NULL| NULL |
> 40 | Table function: json_table |
> +--+-+---+--+---+--+-+--+--++
>
> Note the 'SUBQUERY', that is, the subquery is considered uncorrelated?
> This needs to be investigated.
Ok, I see that the subquery is first marked as correlated but then marked as
non-correlated here:
#0 st_select_lex::update_correlated_cache
#1 st_select_lex::optimize_unflattened_subqueries
#2 JOIN::optimize_unflattened_subqueries
#3 JOIN::optimize_stage2
#4 JOIN::optimize_inner
Apparently, st_select_lex::update_correlated_cache doesn't yet account for
Table Functions. Please fix.
BR
Sergei
--
Sergei Petrunia, Software Developer
MariaDB Corporation | Skype: sergefp | Blog: http://petrunia.net
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