[Commits] a74e3ef17e7: MDEV-14551 Can't find record in table on multi-table update with ORDER BY

Sergey Petrunia sergey at mariadb.com
Thu Apr 12 19:18:43 EEST 2018


Hi Serg,

Please find some cosmetic input below.

(additionally, we've found a failing example while chatting)

On Tue, Apr 10, 2018 at 02:10:17PM +0200, serg at mariadb.org wrote:
> revision-id: a74e3ef17e7a8693d68001290a8d91b5b206804d (mariadb-10.3.5-138-ga74e3ef17e7)
> parent(s): 9bd3af97dffa411657879bbdfd4dfef38c99f7cc
> author: Sergei Golubchik
> committer: Sergei Golubchik
> timestamp: 2018-04-10 14:09:17 +0200
> message:
> 
> MDEV-14551 Can't find record in table on multi-table update with ORDER BY

...
> diff --git a/mysql-test/main/multi_update.test b/mysql-test/main/multi_update.test
> index 5feebe87a5a..96e78dab82b 100644
> --- a/mysql-test/main/multi_update.test
> +++ b/mysql-test/main/multi_update.test
> @@ -914,3 +914,14 @@ update t1 set c1=NULL;
>  update t1, t2 set t1.c1=t2.c3 where t1.c3=t2.c3 order by t1.c3 desc limit 2;
>  select * from t1;
>  drop table t1, t2;
> +
> +#
> +# MDEV-14551 Can't find record in table on multi-table update with ORDER BY
> +#
> +CREATE TABLE t1 (i INT) ENGINE=MEMORY;
> +INSERT t1 VALUES (1),(2);
> +CREATE TABLE t2 (f INT) ENGINE=MyISAM;
> +INSERT t2 VALUES (1),(2);
> +UPDATE t1, t2 SET f = 126 ORDER BY f LIMIT 2;
> +SELECT * FROM t2;
> +DROP TABLE t1, t2;
> diff --git a/sql/item.h b/sql/item.h
> index 9574bdc63bf..e391e7810c4 100644
> --- a/sql/item.h
> +++ b/sql/item.h
> @@ -2023,6 +2023,7 @@ class Item: public Value_source,
>    {
>      marker &= ~EXTRACTION_MASK;
>    }
> +  virtual TABLE *rowid_table() const { return 0; }

I am concerned about this approach bloating class Item's vtable. 

There is (and likely will ever be) only one class with a different 
implementation, the check for this is made only in one place - why not
check Item's type() or functype(), etc?

>  };
>  
>  MEM_ROOT *get_thd_memroot(THD *thd);
> diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
> index c6b0ae7fba8..9097ffca867 100644
> --- a/sql/item_strfunc.cc
> +++ b/sql/item_strfunc.cc
> @@ -5204,3 +5204,23 @@ String *Item_func_dyncol_list::val_str(String *str)
>      my_free(names);
>    return NULL;
>  }
> +
> +Item_temptable_rowid::Item_temptable_rowid(TABLE *table_arg)
> +  : Item_str_func(table_arg->in_use), table(table_arg)
> +{
> +  max_length= table->file->ref_length;
> +}
> +
> +void Item_temptable_rowid::fix_length_and_dec()
> +{
> +  used_tables_cache= table->map;
> +  const_item_cache= false;
> +}
> +
> +String *Item_temptable_rowid::val_str(String *str)
> +{
> +  if (!((null_value= table->null_row)))
> +    table->file->position(table->record[0]);
> +  str_value.set((char*)(table->file->ref), max_length, &my_charset_bin);
> +  return &str_value;
> +}
> diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
> index 18cda491efd..49de5568696 100644
> --- a/sql/item_strfunc.h
> +++ b/sql/item_strfunc.h
> @@ -1748,5 +1748,20 @@ class Item_func_dyncol_list: public Item_str_func
>    { return get_item_copy<Item_func_dyncol_list>(thd, this); }
>  };
>  
> -#endif /* ITEM_STRFUNC_INCLUDED */

Please add a note that this is not the "_rowid" that we support in the parser.

> +class Item_temptable_rowid :public Item_str_func
> +{
> +  TABLE *table;
> +public:
> +  Item_temptable_rowid(TABLE *table_arg);
> +  const Type_handler *type_handler() const { return &type_handler_string; }
> +  Field *create_tmp_field(bool group, TABLE *table)
> +  { return create_table_field_from_handler(table); }
> +  String *val_str(String *str);
> +  const char *func_name() const { return "<rowid>"; }
> +  void fix_length_and_dec();
> +  Item *get_copy(THD *thd)
> +  { return get_item_copy<Item_temptable_rowid>(thd, this); }
> +  TABLE *rowid_table() const { return table; }
> +};
>  
> +#endif /* ITEM_STRFUNC_INCLUDED */
...

> diff --git a/sql/sql_select.cc b/sql/sql_select.cc
> index 796ea569e64..22301319680 100644
> --- a/sql/sql_select.cc
> +++ b/sql/sql_select.cc
> @@ -2650,6 +2650,21 @@ bool JOIN::add_having_as_table_cond(JOIN_TAB *tab)
>  }
>  
>  
> +bool JOIN::add_fields_for_current_rowid(JOIN_TAB *cur, List<Item> *table_fields)

I think ths is actually "current rowids", in plural. As the loop shows, there
are multiple current rowids (from different tables).

> +{
> +  for (JOIN_TAB *tab=join_tab; tab < cur; tab++)

Please add a comment:
this will not walk into semi-join materialization nests but this is ok 
because we will never need to save current rowids for those.

> +  {
> +    if (!tab->keep_current_rowid)
> +      continue;
> +    Item *item= new (thd->mem_root) Item_temptable_rowid(tab->table);
> +    item->fix_fields(thd, 0);
> +    table_fields->push_back(item, thd->mem_root);
> +    cur->tmp_table_param->func_count++;
> +  }
> +  return 0;
> +}
> +
> +
>  /**
>    Set info for aggregation tables
>  
> diff --git a/sql/sql_select.h b/sql/sql_select.h
> index f8911fbba01..1da87bb9d50 100644
> --- a/sql/sql_select.h
> +++ b/sql/sql_select.h
> @@ -1438,6 +1438,9 @@ class JOIN :public Sql_alloc
>    
>    enum { QEP_NOT_PRESENT_YET, QEP_AVAILABLE, QEP_DELETED} have_query_plan;
>  
> +  // if keep_current_rowid=true, whether they should be saved in temporary table
> +  bool tmp_table_keep_current_rowid;
Same input as with add_fields_for_current_rowid - use plural.

> +
>    /*
>      Additional WHERE and HAVING predicates to be considered for IN=>EXISTS
>      subquery transformation of a JOIN object.

> diff --git a/sql/sql_union.cc b/sql/sql_union.cc
> index 0149c2848c2..0e29f817e56 100644
> --- a/sql/sql_union.cc
> +++ b/sql/sql_union.cc
> @@ -507,14 +507,14 @@ void select_union_recursive::cleanup()
>  bool select_union_direct::change_result(select_result *new_result)
>  {
>    result= new_result;
> -  return (result->prepare(unit->types, unit) || result->prepare2());
> +  return (result->prepare(unit->types, unit) || result->prepare2(0));
Do we really continue to use '0' when 'NULL' should be used?  I prefer "NULL".

>  }
>  
>  
>  bool select_union_direct::postponed_prepare(List<Item> &types)
>  {
>    if (result != NULL)
> -    return (result->prepare(types, unit) || result->prepare2());
> +    return (result->prepare(types, unit) || result->prepare2(0));
>    else
>      return false;
>  }
> diff --git a/sql/sql_update.cc b/sql/sql_update.cc
> index 38638d3aa1d..4ae7e33b4e3 100644
> --- a/sql/sql_update.cc
> +++ b/sql/sql_update.cc
> @@ -2205,10 +2195,41 @@ multi_update::initialize_tables(JOIN *join)
>        DBUG_RETURN(1);
>      tmp_tables[cnt]->file->extra(HA_EXTRA_WRITE_CACHE);
>    }
> +  join->tmp_table_keep_current_rowid= TRUE;
>    DBUG_RETURN(0);
>  }
>  

(Follwing explanations on Slack) Please add a comment there, saying that

Here we walk through the aggegation temptable to find where rowids 
are stored.

And then for each of the multi-update tables, we get them to copy the data from
the rowid field in the aggregation temptable.


> +
> +int multi_update::prepare2(JOIN *join)
> +{
> +  if (!join->need_tmp || !join->tmp_table_keep_current_rowid)
> +    return 0;
> +
> +  // there cannot be many tmp tables in multi-update
> +  JOIN_TAB *tmptab= join->join_tab + join->exec_join_tab_cnt();
> +
> +  for (Item **it= tmptab->tmp_table_param->items_to_copy; *it ; it++)
> +  {
> +    TABLE *tbl= (*it)->rowid_table();
> +    if (!tbl)
> +      continue;
> +    for (uint i= 0; i < table_count; i++)
> +    {
> +      for (Item **it2= tmp_table_param[i].items_to_copy; *it2; it2++)
> +      {
> +        if ((*it2)->rowid_table() != tbl)
> +          continue;
> +        *it2= new (thd->mem_root) Item_field(thd, (*it)->get_tmp_table_field());
> +        if (!*it2)
> +          return 1;
> +      }
> +    }
> +  }
> +  return 0;
> +}
> +
> +
>  multi_update::~multi_update()
>  {
>    TABLE_LIST *table;

BR
 Sergei
-- 
Sergei Petrunia, Software Developer
MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog




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