[Commits] Review for: b4696ee97e684 : MDEV-15777: Support Early NULLs filtering-like restrictions in the range optimizer

varun gupta varunraiko1803 at gmail.com
Thu May 23 17:31:48 EEST 2019


On Wed, May 22, 2019 at 9:44 PM Sergey Petrunia <sergey at mariadb.com> wrote:

> Hi Varun,
>
> Please find review input below. Only cosmetic changes are requested.
>
> I also assume that after this is pushed
> - we add a optimizer trace printout into 10.4
>
has created MDEV-19567 for this

> - the feature is enabled by default in 10.5
>
let us decide the name of the optimizer flag and then I will create the
issue for this

> ?  (do we need separate MDEVs for this?)
>
> One final question is the choice of name for @@optimizer_switch flag. Let
> me get back to
> you on this.
>
> > commit b4696ee97e6846ba49ef203cfc7189f50c1e53a7
> > Author: Varun Gupta <varun.gupta at mariadb.com>
> > Date:   Mon May 20 15:14:30 2019 +0530
> >
> >     MDEV-15777: Support Early NULLs filtering-like restrictions in the
> range optimizer
> >
> >     For eqjoin conditions, we add a NOT NULL predicate so as to allow
> the range optimizer
> >     to use the predicate and possibly create a range access on the given
> table.
> >
> >     Example:
> >       select * from t1,t2 where t1.a=t2.a;  we have KEY(a) on t1
> >       we would inject a NOT NULL predicate t1.a IS NOT NULL for table t1
> >       this would allow the range optimizer to create ranges and we get a
> >       range access on table t1, then we will be able
> >       to do an early NULL filtering for ranges too.
> >
> > diff --git a/mysql-test/main/range.result b/mysql-test/main/range.result
> > index 32e0cf2868c..d75d6734277 100644
> > --- a/mysql-test/main/range.result
> > +++ b/mysql-test/main/range.result
> > @@ -3024,3 +3024,151 @@ drop table t1;
> >  #
> >  # End of 10.2 tests
> >  #
> > +#
> > +# MDEV-15777: Support Early NULLs filtering-like restrictions in the
> range optimizer
> > +#
> > +set @save_optimizer_switch= @@optimizer_switch;
> > +set @@optimizer_switch='null_rejecting_for_ranges=on';
> > +create table ten(a int);
> > +insert into ten values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
> > +create table one_k(a int);
> > +insert into one_k select A.a + B.a* 10 + C.a * 100 from ten A, ten B,
> ten C;
>
> Did we abandon the convention of naming the tables t1,t2,t3,... ?
> If not, please rename.
>
As decided,  I have kept this the same

>
> > +create table t1 (
> > +id int(10) unsigned NOT NULL,
> > +subset_id int(11) DEFAULT NULL,
> > +PRIMARY KEY (id),
> > +KEY t1_subset_id (subset_id));
> ...
>
> > diff --git a/sql/opt_range.cc b/sql/opt_range.cc
> > index ec7b3dbbd7a..cb7800d1ba6 100644
> > --- a/sql/opt_range.cc
> > +++ b/sql/opt_range.cc
> > @@ -2539,6 +2546,42 @@ int SQL_SELECT::test_quick_select(THD *thd,
> key_map keys_to_use,
> >      TRP_GROUP_MIN_MAX *group_trp;
> >      double best_read_time= read_time;
> >
> > +    /*
> > +      For the range optimizer, null_rejecting_conds are just an extra
> condition
> > +      on which one can use index to create ranges.
> > +
> > +      Also here we try to allow consider range access for a column
> involed in a
> > +      null rejecting predicate only if it is the first keypart of an
> index.
> > +      Let try to make it clear with examples:
> > +
> > +      Query 1
> > +        select * from t1,t2 where t1.a=2 and t1.b=t2.b;
> > +        and we have a key(a,b)
> > +        So lets consider range access for table t1:
> > +        Null rejecting predicate : t1.b IS NOT NULL
> > +        but the column t1.b is NOT the first keypart in the index,
> > +        so we don't consider it while building ranges
> > +
> > +      Query 2
> > +        select * from t1,t2 where t1.a=t2.a and t1.b=t2.b;
> > +        and we have a key (a,b)
> > +
> > +        So lets consider range access for table t1:
> > +        Null rejecting predicate : t1.a IS NOT NULL AND t1.b IS NOT NULL
> > +        so here t1.a is the first keypart in the index, so we consider
> > +        the predicate for building the ranges.
> > +
> > +        The first keypart prerequisite is made as we try to reuse range
> > +        estimates (because they are more accurate) at different places
> > +        and we needed to make sure that correct/accurate estimates are
> used there.
> > +    */
> > +
> > +    if (null_rejecting_conds)
> > +      not_null_cond_tree= null_rejecting_conds->get_mm_tree(&param,
> > +
> &null_rejecting_conds);
> Please fix indentation and fit within 80 chars. ^
> And also use curly braces as the code inside if doesn't fit on one line.
>
Done

>
> > +    if (not_null_cond_tree)
> > +      remove_nonrange_trees(&param, not_null_cond_tree);
> > +
> >      if (cond)
> >      {
> >        if ((tree= cond->get_mm_tree(&param, &cond)))
> > @@ -2557,6 +2600,7 @@ int SQL_SELECT::test_quick_select(THD *thd,
> key_map keys_to_use,
> >            tree= NULL;
> >        }
> >      }
> > +    tree= tree_and(&param, tree, not_null_cond_tree);
> >
> >      /*
> >        Try to construct a QUICK_GROUP_MIN_MAX_SELECT.
> > @@ -4422,6 +4466,128 @@ static bool
> create_partition_index_description(PART_PRUNE_PARAM *ppar)
> >    return FALSE;
> >  }
> >
> > +inline void add_cond(THD *thd, Item **e1, Item *e2)
> > +{
> > +  if (*e1)
> > +  {
> > +    if (!e2)
> > +      return;
> > +    Item *res;
> > +    if ((res= new (thd->mem_root) Item_cond_and(thd, *e1, e2)))
> > +    {
> > +      res->fix_fields(thd, 0);
> > +      res->update_used_tables();
> > +      *e1= res;
> > +    }
> > +  }
> > +  else
> > +    *e1= e2;
> > +}
> > +
> > +/*
> > +  Create null rejecting conditions for a table, for all the equalites
> > +  present in the WHERE clause of a query.
> > +
> > +  SYNOPSIS
> > +    make_null_rejecting_conds()
> > +    @param TABLE        - Keys of this table will participate in null
> > +                          rejecting conditions
> > +    @param keyuse_array - array that has all the equalites of the
> > +                          WHERE clasuse
>
> The above doesn't match the function's definition. Out of date comment?
>
Done

> > +
> > +  DESCRIPTION
> > +    This function creates null rejecting conditions for a table. These
> > +    conditions are created to do range analysis on them , the conditions
> > +    are of the form tbl.key.keypart IS NOT NULL.
> > +
> > +  IMPLEMENTATION
> > +    Lookup in the keyuse array to check if it has equalites that belong
> > +    to the given table. If yes then find out if the conditions are null
> > +    rejecting and accordingly create all the condition for the keys of a
> > +    given table and AND them.
> > +
> > +
> > +  RETURN
> > +    NOT NULL - Found null rejecting conditions for the given table
> > +    NULL - No null rejecting conditions for the given table
> The above doesn't match the function's definition. Out of date comment?
>
removed this and also fixed the typos for the comments in IMPLEMENTATION

> > +*/
> > +
> > +void make_null_rejecting_conds(THD *thd, JOIN_TAB *tab)
> > +{
> > +  KEY *keyinfo;
> > +  Item *cond= NULL;
> > +  KEYUSE* keyuse;
> > +  TABLE *table= tab->table;
> > +  key_map *const_keys= &tab->const_keys;
> ^ Does it make sense to introduce a variable if it is only used once?

 Removed the variable here

> > +
> > +  /*
> > +    No need to add NOT NULL condition for materialized derived tables
> > +    or materialized subqueries as we do not run the range optimizer
> > +    on their conditions
> > +  */
> > +
> > +  if (!optimizer_flag(thd, OPTIMIZER_SWITCH_NULL_REJECTING_FOR_RANGES))
> > +    return;
> > +
> > +  if (tab->table->is_filled_at_execution() ||
> > +      (tab->table->pos_in_table_list->derived &&
> > +       tab->table->pos_in_table_list->is_materialized_derived()))
> > +    return;
> > +
> > +  Field_map not_null_keypart_map;
> > +
> > +  /*
> > +    The null rejecting conds added will be on the keypart of a key, so
> for
> > +    that we need the table to atleast have a key.
> > +  */
> > +  if (!table->s->keys || table->null_rejecting_conds || !tab->keyuse)
> > +    return;
> > +
> > +  for(keyuse= tab->keyuse; keyuse->table == table; keyuse++)
> > +  {
> Please add space, "for ".

 Done

> > +    /*
> > +      No null rejecting conds for a hash key or full-text keys
> > +    */
> > +    if (keyuse->key == MAX_KEY || keyuse->keypart == FT_KEYPART)
> > +      continue;
> > +    keyinfo= keyuse->table->key_info + keyuse->key;
> > +    Field *field= keyinfo->key_part[keyuse->keypart].field;
> > +
> > +    if (not_null_keypart_map.is_set(field->field_index))
> > +      continue;
> > +
> > +    /*
> > +      No need to add null-rejecting condition if we have a
> > +      keyuse element as
> > +        - table.key.keypart= const
> > +        - (table.key.keypart= tbl.otherfield or table.key.keypart IS
> NULL)
> > +        - table.key.keypart IS NOT NULLABLE
> > +    */
> > +
> > +    if (keyuse->val->const_item() ||
> > +        !(keyuse->null_rejecting && field->maybe_null()) ||
> > +        keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL)
> > +      continue;
> > +
> > +    Item_field *field_item= new (thd->mem_root)Item_field(thd, field);
> > +    Item* not_null_item= new (thd->mem_root)Item_func_isnotnull(thd,
> field_item);
> > +
> > +    /*
> > +      adding the key to const keys as we have the condition
> > +      as key.keypart IS NOT NULL
> > +    */
> > +
> > +    const_keys->set_bit(keyuse->key);
> > +    not_null_item->fix_fields(thd, 0);
> ^^ please change 0 to &not_null_item.
>
Done

> > +    not_null_item->update_used_tables();
> > +    add_cond(thd, &cond, not_null_item);
> > +    not_null_keypart_map.set_bit(field->field_index);
> > +  }
> > +  DBUG_EXECUTE("where", print_where(cond, "Early Null Filtering",
> > +                                    QT_ORDINARY););
> > +  table->null_rejecting_conds= cond;
> > +}
> > +
> >
> >  #ifndef DBUG_OFF
> >
> ...
> > diff --git a/sql/sql_select.cc b/sql/sql_select.cc
> > index 8cdcf3afc8b..140ceed5c2d 100644
> > --- a/sql/sql_select.cc
> > +++ b/sql/sql_select.cc
> > @@ -5510,15 +5512,30 @@ add_key_field(JOIN *join,
> >      If the condition has form "tbl.keypart = othertbl.field" and
> >      othertbl.field can be NULL, there will be no matches if
> othertbl.field
> >      has NULL value.
> > -    We use null_rejecting in add_not_null_conds() to add
> > -    'othertbl.field IS NOT NULL' to tab->select_cond.
> > +
> > +    The field KEY_FIELD::null_rejecting is set to TRUE if either
> > +    the left or the right hand side of the equality is NULLABLE
> > +
> > +    null_rejecting is used
> > +      - by add_not_null_conds(), to add "othertbl.field IS NOT NULL" to
> > +        othertbl's tab->select_cond. (This is called "Early NULLs
> filtering")
> > +
> > +      - by make_null_rejecting_conds(), to provide range optimizer with
> > +        additional "tbl.keypart IS NOT NULL" condition.
> >    */
> >    {
> >      Item *real= (*value)->real_item();
> > -    if (((cond->functype() == Item_func::EQ_FUNC) ||
> > -         (cond->functype() == Item_func::MULT_EQUAL_FUNC)) &&
> > -        (real->type() == Item::FIELD_ITEM) &&
> > -        ((Item_field*)real)->field->maybe_null())
> > +    if ((
> > +         (cond->functype() == Item_func::EQ_FUNC) ||
> > +         (cond->functype() == Item_func::MULT_EQUAL_FUNC)
> > +        ) &&
> > +        (
> > +          (
> > +            (real->type() == Item::FIELD_ITEM) &&
> > +            ((Item_field*)real)->field->maybe_null()
> > +          ) ||
> > +          (field->maybe_null())
> > +        ))
> >        (*key_fields)->null_rejecting= true;
> >      else
> >        (*key_fields)->null_rejecting= false;
> > @@ -9982,8 +9999,12 @@ static bool create_ref_for_key(JOIN *join,
> JOIN_TAB *j,
> >        uint maybe_null= MY_TEST(keyinfo->key_part[i].null_bit);
> >        j->ref.items[i]=keyuse->val;           // Save for cond removal
> >        j->ref.cond_guards[i]= keyuse->cond_guard;
> > -      if (keyuse->null_rejecting)
> > +      Item *real= (keyuse->val)->real_item();
> > +      if (keyuse->null_rejecting &&
> > +          (real->type() == Item::FIELD_ITEM) &&
> > +          ((Item_field*)real)->field->maybe_null())
>
> This code looks as if
>
>   if keyuse->val->maybe_null() != keyuse->val->real_item()->maybe_null()
>
> do you have any specific case in mind or this is just to match the code in
> add_key_field?
>

In add_key_field for a keyuse
 c=a ( a is a primary key, so a IS NOT NULL)
we check if either the left or right hand side is null_rejecting or not, if
yes then we set
null_rejecting= true else false
So in add_not_null_conds, we check if we want to add a NOT NULL predicate
for the keyuse, so we need to check if the right hand side of the
keyuse(that is 'a') is NULLABLE or not, if yes only then we will add the
null_rejecting predicate


> >          j->ref.null_rejecting|= (key_part_map)1 << i;
> > +
> >        keyuse_uses_no_tables= keyuse_uses_no_tables &&
> !keyuse->used_tables;
> >        /*
> >          We don't want to compute heavy expressions in EXPLAIN, an
> example would
>
> BR
>  Sergei
> --
> Sergei Petrunia, Software Developer
> MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog
>
>
> BR,
Varun
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