Hi Alexey, On Mon, Sep 14, 2020 at 03:38:38PM +0400, Alexey Botchkov wrote: > Hi, Sergei!. > > so the branch name is 'bb-mdef17399-hf'. > It has slightly changed since last patch so please pay attention. > > There i present the patch that resolves issues that you mentioned > in your last comments. > One important is not fixed though. > That is: > CREATE TABLE t1(id INT, f1 JSON); > INSERT INTO t1 VALUES (1, '{\"1\": 1}'), (2, '{\"1\": 2}'), (3, '{\"1\": > 3}'), > (4, '{\"1\": 4}'), (5, '{\"1\": 5}'), (6, '{\"1\": 6}'); > > SELECT * FROM t1 WHERE id IN > (SELECT id FROM t1 as tt2, > JSON_TABLE(f1, "$" COLUMNS (jf FOR ORDINALITY)) AS tbl); > > That SELECT crashes in the optimizer, as the greedy_search() can't find any > satisfying plan. > I got rid of the crash with this line: > @@ -9520,7 +9528,7 @@ best_extension_by_limited_search(JOIN *join, > table_map real_table_bit= s->table->map; > if ((remaining_tables & real_table_bit) && > (allowed_tables & real_table_bit) && > - !(remaining_tables & s->dependent) && > +// !(remaining_tables & s->dependent) && > > But i don't mean it's an acceptable fix. > > It seems to me the problem is in the optimizer, so i'd like to ask your > opinion. > Maybe you just know the answer at once.
After some debugging I see that the following happens: 1. Execution reaches Table_function_json_table::setup It computes m_dep_tables= m_json->used_tables(); this is =1 (In the subquery, table tt2 has map=1) 2. Then, subquery is converted into a semi-join. That is, it is merged into its parent subquery. There, we have: table t1: map=1 table tt2: map=2 table JSON_TABLE(...) AS tbl: map=3 3. The subquery was uncorrelated, so SJ-Materialization is a possible option and the join optimizer attempts to construct a join order for the subquery tables. However it can't succeed, as the table "JSON_TABLE(..) AS tbl" is set to be dependent on table with map=1, which is not put into the join order because it is not a part of subquery. As a result, we get assertion failure when the optimizer fails to produce any join orders. The probem here is on step #2. When the subquery's tables are moved to the parent query, they get new values of TABLE::map, and also all their attributes that contain table maps need to be updated. This done here in convert_subq_to_sj() function: ``` /* n. Walk through child's tables and adjust table->map */ List_iterator_fast<TABLE_LIST> si(subq_lex->leaf_tables); while ((tl= si++)) { tl->set_tablenr(table_no); if (tl->is_jtbm()) { tl->jtbm_table_no= table_no; Item *dummy= tl->jtbm_subselect; tl->jtbm_subselect->fix_after_pullout(parent_lex, &dummy, true); ``` In that code one can see: if the subquery has table that has 'is_jtbm()==true', then ... some processing is done to re-compute its attributes after the table has been pulled up into the parent select. The same should be done for TABLE_LIST elements that are JSON_TABLE(..). If you'll introduce a new function, fix_after_pullout() is a good name. It is already used for Item-derived classes. > If not, i'll dig into it. > And you're welcome to observe the new patch. > > Best regards. > HF -- BR Sergei -- Sergei Petrunia, Software Developer MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : maria-developers@lists.launchpad.net Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp