Skip to content

M
mariadb
Commit d294aae6 authored by Sergey Petrunya's avatar Sergey Petrunya
Browse files
Options

MWL#17: Table elimination: last fixes 

- Add an @@optimizer_switch flag for table_elimination for debug build
- Better comments 

mysql-test/t/index_merge_myisam.test:
  MWL#17: Table elimination: last fixes
  - Add an @@optimizer_switch flag for table_elimination for debug build
sql/mysql_priv.h:
  MWL#17: Table elimination: last fixes
  - Add an @@optimizer_switch flag for table_elimination for debug build
sql/mysqld.cc:
  MWL#17: Table elimination: last fixes
  - Add an @@optimizer_switch flag for table_elimination for debug build
parent 21d25739
Hide whitespace changes
Inline Side-by-side
Showing with 169 additions and 84 deletions
mysql-test/t/index_merge_myisam.test
View file @ d294aae6
......@@ -25,15 +25,19 @@ let $merge_table_support= 1;
--echo # we get another @@optimizer_switch user)
--echo #
--replace_regex /,table_elimination=on//
select @@optimizer_switch;
set optimizer_switch='index_merge=off,index_merge_union=off';
--replace_regex /,table_elimination=on//
select @@optimizer_switch;
set optimizer_switch='index_merge_union=on';
--replace_regex /,table_elimination=on//
select @@optimizer_switch;
set optimizer_switch='default,index_merge_sort_union=off';
--replace_regex /,table_elimination=on//
select @@optimizer_switch;
--error ER_WRONG_VALUE_FOR_VAR
......@@ -71,17 +75,21 @@ set optimizer_switch='default,index_merge=on,index_merge=off,default';
set optimizer_switch=default;
set optimizer_switch='index_merge=off,index_merge_union=off,default';
--replace_regex /,table_elimination=on//
select @@optimizer_switch;
set optimizer_switch=default;
# Check setting defaults for global vars
--replace_regex /,table_elimination=on//
select @@global.optimizer_switch;
set @@global.optimizer_switch=default;
--replace_regex /,table_elimination=on//
select @@global.optimizer_switch;
--echo #
--echo # Check index_merge's @@optimizer_switch flags
--echo #
--replace_regex /,table_elimination.on//
select @@optimizer_switch;
create table t0 (a int);
......@@ -182,6 +190,7 @@ set optimizer_switch='default,index_merge_union=off';
explain select * from t1 where a=10 and b=10 or c=10;
set optimizer_switch=default;
--replace_regex /,table_elimination.on//
show variables like 'optimizer_switch';
drop table t0, t1;
......
sql/mysql_priv.h
View file @ d294aae6
......@@ -528,14 +528,27 @@ protected:
#define OPTIMIZER_SWITCH_INDEX_MERGE_UNION 2
#define OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION 4
#define OPTIMIZER_SWITCH_INDEX_MERGE_INTERSECT 8
#define OPTIMIZER_SWITCH_LAST 16
/* The following must be kept in sync with optimizer_switch_str in mysqld.cc */
#define OPTIMIZER_SWITCH_DEFAULT (OPTIMIZER_SWITCH_INDEX_MERGE | \
OPTIMIZER_SWITCH_INDEX_MERGE_UNION | \
OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION | \
OPTIMIZER_SWITCH_INDEX_MERGE_INTERSECT)
#ifdef DBUG_OFF
# define OPTIMIZER_SWITCH_LAST 16
#else
# define OPTIMIZER_SWITCH_TABLE_ELIMINATION 16
# define OPTIMIZER_SWITCH_LAST 32
#endif
#ifdef DBUG_OFF
/* The following must be kept in sync with optimizer_switch_str in mysqld.cc */
# define OPTIMIZER_SWITCH_DEFAULT (OPTIMIZER_SWITCH_INDEX_MERGE | \
OPTIMIZER_SWITCH_INDEX_MERGE_UNION | \
OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION | \
OPTIMIZER_SWITCH_INDEX_MERGE_INTERSECT)
#else
# define OPTIMIZER_SWITCH_DEFAULT (OPTIMIZER_SWITCH_INDEX_MERGE | \
OPTIMIZER_SWITCH_INDEX_MERGE_UNION | \
OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION | \
OPTIMIZER_SWITCH_INDEX_MERGE_INTERSECT | \
OPTIMIZER_SWITCH_TABLE_ELIMINATION)
#endif
/*
Replication uses 8 bytes to store SQL_MODE in the binary log. The day you
......
sql/mysqld.cc
View file @ d294aae6
......@@ -297,9 +297,14 @@ TYPELIB sql_mode_typelib= { array_elements(sql_mode_names)-1,"",
static const char *optimizer_switch_names[]=
{
"index_merge","index_merge_union","index_merge_sort_union",
"index_merge_intersection", "default", NullS
"index_merge","index_merge_union","index_merge_sort_union",
"index_merge_intersection",
#ifndef DBUG_OFF
"table_elimination",
#endif
"default", NullS
};
/* Corresponding defines are named OPTIMIZER_SWITCH_XXX */
static const unsigned int optimizer_switch_names_len[]=
{
......@@ -307,6 +312,9 @@ static const unsigned int optimizer_switch_names_len[]=
sizeof("index_merge_union") - 1,
sizeof("index_merge_sort_union") - 1,
sizeof("index_merge_intersection") - 1,
#ifndef DBUG_OFF
sizeof("table_elimination") - 1,
#endif
sizeof("default") - 1
};
TYPELIB optimizer_switch_typelib= { array_elements(optimizer_switch_names)-1,"",
......@@ -382,7 +390,10 @@ static const char *sql_mode_str= "OFF";
/* Text representation for OPTIMIZER_SWITCH_DEFAULT */
static const char *optimizer_switch_str="index_merge=on,index_merge_union=on,"
"index_merge_sort_union=on,"
"index_merge_intersection=on";
"index_merge_intersection=on"
#ifndef DBUG_OFF
",table_elimination=on";
#endif
static char *mysqld_user, *mysqld_chroot, *log_error_file_ptr;
static char *opt_init_slave, *language_ptr, *opt_init_connect;
static char *default_character_set_name;
......@@ -6929,8 +6940,11 @@ The minimum value for this variable is 4096.",
0, GET_ULONG, OPT_ARG, MAX_TABLES+1, 0, MAX_TABLES+2, 0, 1, 0},
{"optimizer_switch", OPT_OPTIMIZER_SWITCH,
"optimizer_switch=option=val[,option=val...], where option={index_merge, "
"index_merge_union, index_merge_sort_union, index_merge_intersection} and "
"val={on, off, default}.",
"index_merge_union, index_merge_sort_union, index_merge_intersection"
#ifndef DBUG_OFF
", table_elimination"
#endif
"} and val={on, off, default}.",
(uchar**) &optimizer_switch_str, (uchar**) &optimizer_switch_str, 0, GET_STR, REQUIRED_ARG,
/*OPTIMIZER_SWITCH_DEFAULT*/0,
0, 0, 0, 0, 0},
......
sql/opt_table_elimination.cc
View file @ d294aae6
......@@ -18,6 +18,7 @@
/*
OVERVIEW
========
This file contains table elimination module. The idea behind table
elimination is as follows: suppose we have a left join
......@@ -36,7 +37,9 @@
null-complemented one) and we don't care about what that record combination
is.
MODULE INTERFACE
================
The module has one entry point - eliminate_tables() function, which one
needs to call (once) at some point before the join optimization.
......@@ -58,23 +61,25 @@
Table elimination is redone on every PS re-execution.
TABLE ELIMINATION ALGORITHM FOR ONE OUTER JOIN
==============================================
As said above, we can remove inner side of an outer join if it is
As described above, we can remove inner side of an outer join if it is
1. not referred to from any other parts of the query
2. always produces one matching record combination.
We check #1 by doing a recursive descent down the join->join_list while
maintaining a union of used_tables() attribute of all expressions we've seen
"elsewhere". When we encounter an outer join, we check if the bitmap of
tables on its inner side has an intersection with tables that are used
We check #1 by doing a recursive descent down the join->join_list while
maintaining a union of used_tables() attribute of all Item expressions in
other parts of the query. When we encounter an outer join, we check if the
bitmap of tables on its inner side has intersection with tables that are used
elsewhere. No intersection means that inner side of the outer join could
potentially be eliminated.
In order to check #2, one needs to prove that inner side of an outer join
is functionally dependent on the outside. We prove dependency by proving
functional dependency of intermediate objects:
is functionally dependent on the outside. The proof is constructed from
functional dependencies of intermediate objects:
- Inner side of outer join is functionally dependent when each of its tables
are functionally dependent. (We assume a table is functionally dependent
......@@ -91,14 +96,15 @@
where expr is functionally-depdendent.
Apparently the above rules can be applied recursively. Also, certain entities
depend on multiple other entities. We model this by a bipartite graph which
has two kinds of nodes:
These relationships are modeled as a bipartite directed graph that has
dependencies as edges and two kinds of nodes:
Value nodes:
- Table column values (each is a value of tblX.columnY)
- Table nodes (each node represents a table inside an eliminable join nest).
each value is either bound (i.e. functionally dependent) or not.
- Table values (each node represents a table inside the join nest we're
trying to eliminate).
A value has one attribute, it is either bound (i.e. functionally dependent)
or not.
Module nodes:
- Modules representing tblX.colY=expr equalities. Equality module has
......@@ -118,11 +124,54 @@
(their expressions are either constant or depend only on tables that are
outside of the outer join in question) and performns a breadth-first
traversal. If we reach the outer join nest node, it means outer join is
functionally-dependant and can be eliminated. Otherwise it cannot.
functionally-dependant and can be eliminated. Otherwise it cannot be.
HANDLING MULTIPLE NESTED OUTER JOINS
(TODO : explanations why 'local bottom up is sufficient')
HANDLING MULTIPLE NESTED OUTER JOINS
====================================
Outer joins that are not nested one within another are eliminated
independently. For nested outer joins we have the following considerations:
1. ON expressions from children outer joins must be taken into account
Consider this example:
SELECT t0.*
FROM
t0
LEFT JOIN
(t1 LEFT JOIN t2 ON t2.primary_key=t1.col1)
ON
t1.primary_key=t0.col AND t2.col1=t1.col2
Here we cannot eliminate the "... LEFT JOIN t2 ON ..." part alone because the
ON clause of top level outer join has references to table t2.
We can eliminate the entire "... LEFT JOIN (t1 LEFT JOIN t2) ON .." part,
but in order to do that, we must look at both ON expressions.
2. ON expressions of parent outer joins are useless.
Consider an example:
SELECT t0.*
FROM
t0
LEFT JOIN
(t1 LEFT JOIN t2 ON some_expr)
ON
t2.primary_key=t1.col -- (*)
Here the uppermost ON expression has a clause that gives us functional
dependency of table t2 on t1 and hence could be used to eliminate the
"... LEFT JOIN t2 ON..." part.
However, we would not actually encounter this situation, because before the
table elimination we run simplify_joins(), which, among other things, upon
seeing a functional dependency condition like (*) will convert the outer join
of
"... LEFT JOIN t2 ON ..."
into inner join and thus make table elimination not to consider eliminating
table t2.
*/
class Value_dep;
......@@ -157,7 +206,7 @@ public:
/*
A table field value. There is exactly only one such object for any tblX.fieldY
- the field epends on its table and equalities
- the field depends on its table and equalities
- expressions that use the field are its dependencies
*/
class Field_value : public Value_dep
......@@ -175,26 +224,23 @@ public:
field_index
*/
Field_value *next_table_field;
/*
Offset of our part of the bitmap psergey-todo: better comment!
/*
Offset to bits in Func_dep_analyzer::expr_deps
*/
uint bitmap_offset;
/*
Field became known. Check out
- unique keys we belong to
- expressions that depend on us.
*/
void now_bound(Func_dep_analyzer *fda, Module_dep **bound_modules);
void signal_from_field_to_exprs(Func_dep_analyzer* fda,
Module_dep **bound_modules);
};
/*
A table value. There is one Table_value object for every table that can
potentially be eliminated.
Dependencies:
- table depends on any of its unique keys
- has its fields and embedding outer join as dependency.
- has its fields and embedding outer join as dependency
*/
class Table_value : public Value_dep
{
......@@ -205,13 +251,13 @@ public:
TABLE *table;
Field_value *fields; /* Ordered list of fields that belong to this table */
Key_module *keys; /* Ordered list of Unique keys in this table */
//Outer_join_module *outer_join_dep;
void now_bound(Func_dep_analyzer *fda, Module_dep **bound_modules);
};
/*
A 'module'. Module has dependencies
A 'module'. Module has unsatisfied dependencies, number of whose is stored in
unknown_args. Modules also can be linked together in a list.
*/
class Module_dep : public Sql_alloc
......@@ -232,10 +278,11 @@ public:
/*
This represents either
- "tbl.column= expr" equality dependency, i.e. tbl.column depends on fields
- "tbl.column= expr" equality dependency, i.e. tbl.column depends on fields
used in the expression, or
- tbl1.col1=tbl2.col2=... multi-equality.
*/
class Equality_module : public Module_dep
{
public:
......@@ -314,7 +361,11 @@ public:
/* Element for the outer join we're attempting to eliminate */
Outer_join_module *outer_join_dep;
/* Bitmap of how expressions depend on bits */
/*
Bitmap of how expressions depend on bits. Given a Field_value object,
one can check bitmap_is_set(expr_deps, field_val->bitmap_offset + expr_no)
to see if expression equality_mods[expr_no] depends on the given field.
*/
MY_BITMAP expr_deps;
};
......@@ -453,11 +504,23 @@ void build_eq_mods_for_cond(Func_dep_analyzer *fda, Equality_module **eq_mod,
}
case Item_func::MULT_EQUAL_FUNC:
{
/*
The condition is a
tbl1.field1 = tbl2.field2 = tbl3.field3 [= const_expr]
multiple-equality. Do two things:
- Collect an ordered List<Field_value> of tblX.colY where tblX is one
of those that we're trying to eliminate.
- rembember if there was a const_expr or tblY.colZ that we can consider
bound.
Store all collected information in a Equality_module object.
*/
Item_equal *item_equal= (Item_equal*)cond;
List<Field_value> *fvl;
if (!(fvl= new List<Field_value>))
break;
Item_equal_iterator it(*item_equal);
Item_field *item;
Item *bound_item= item_equal->get_const();
......@@ -554,9 +617,9 @@ Equality_module *merge_func_deps(Equality_module *start, Equality_module *new_fi
Equality_module *end, uint and_level)
{
if (start == new_fields)
return start; // Impossible or
return start; /* (nothing) OR (...) -> (nothing) */
if (new_fields == end)
return start; // No new fields, skip all
return start; /* (...) OR (nothing) -> (nothing) */
Equality_module *first_free=new_fields;
......@@ -564,28 +627,6 @@ Equality_module *merge_func_deps(Equality_module *start, Equality_module *new_fi
{
for (Equality_module *old=start ; old != first_free ; old++)
{
/*
Merge multiple-equalities:
A: YES.
(a=b=c) OR (a=b=d) produce "a=b".
TODO:
sort by (table_ptr, column_index)
then run along the two and produce an intersection
Q: What about constants?
a=b=3 OR a=b=5 -> a=b= (either 3 or 5)
a=b OR a=b=5 -> a=b= (any constant)
A: keep the constant iff it is present in both sides and is the same.
class Multi_equality
{
Item *const_item;
List<...) list;
};
*/
if (old->field == new_fields->field)
{
if (!old->field)
......@@ -616,7 +657,7 @@ Equality_module *merge_func_deps(Equality_module *start, Equality_module *new_fi
}
else
{
// no single constant/bound item.
/* no single constant/bound item. */
old->expression= NULL;
}
......@@ -975,7 +1016,7 @@ bool setup_equality_modules_deps(Func_dep_analyzer *fda,
}
else
{
/* It's a multi-equality*/
/* It's a multi-equality */
eq_mod->unknown_args= !test(eq_mod->expression);
List_iterator<Field_value> it(*eq_mod->mult_equal_fields);
Field_value* field_val;
......@@ -1050,6 +1091,11 @@ void eliminate_tables(JOIN *join)
if (!join->outer_join)
DBUG_VOID_RETURN;
#ifndef DBUG_OFF
if (!optimizer_flag(thd, OPTIMIZER_SWITCH_TABLE_ELIMINATION))
DBUG_VOID_RETURN;
#endif
/* Find the tables that are referred to from WHERE/HAVING */
used_tables= (join->conds? join->conds->used_tables() : 0) |
(join->having? join->having->used_tables() : 0);
......@@ -1188,7 +1234,7 @@ eliminate_tables_for_list(JOIN *join, List<TABLE_LIST> *join_list,
/*
Check if condition makes the a set of tables functionally-dependent
Check if given condition makes given set of tables functionally-dependent
SYNOPSIS
check_func_dependency()
......@@ -1197,8 +1243,8 @@ eliminate_tables_for_list(JOIN *join, List<TABLE_LIST> *join_list,
cond Condition to use
DESCRIPTION
Check if condition allows to conclude that the table set is functionally
dependent on everything else.
Check if we can use given condition to infer that the set of given tables
is functionally-dependent on everything else.
RETURN
TRUE - Yes, functionally dependent
......@@ -1216,7 +1262,10 @@ bool check_func_dependency(JOIN *join,
Func_dep_analyzer fda(join);
/* Start value */
/*
Pre-alloc some Equality_module structures. We don't need this to be
guaranteed upper bound.
*/
fda.n_equality_mods_alloced=
join->thd->lex->current_select->max_equal_elems +
(join->thd->lex->current_select->cond_count+1)*2 +
......@@ -1249,7 +1298,7 @@ bool check_func_dependency(JOIN *join,
fda.usable_tables= dep_tables;
/*
Analyze the the ON expression and create Equality_module objects and
Field_value objects for their left parts.
Field_value objects for the used fields.
*/
uint and_level=0;
build_eq_mods_for_cond(&fda, &last_eq_mod, &and_level, cond);
......@@ -1264,14 +1313,14 @@ bool check_func_dependency(JOIN *join,
DBUG_EXECUTE("test", dbug_print_deps(&fda); );
/* The running wave algorithm itself: */
/* The forward running wave algorithm: */
Value_dep *bound_values= NULL;
while (bound_modules)
{
for (;bound_modules; bound_modules= bound_modules->next)
{
if (bound_modules->now_bound(&fda, &bound_values))
return TRUE; /* Dependent! */
return TRUE; /* Dependent */
}
for (;bound_values; bound_values=bound_values->next)
bound_values->now_bound(&fda, &bound_modules);
......@@ -1280,17 +1329,12 @@ bool check_func_dependency(JOIN *join,
}
/*
Table is known means that
- one more element in outer join nest is known
- all its fields are known
*/
void Table_value::now_bound(Func_dep_analyzer *fda,
Module_dep **bound_modules)
{
DBUG_PRINT("info", ("table %s is now bound", table->alias));
/* Signal to all fields that they are now bound */
for (Field_value *field_dep= fields; field_dep;
field_dep= field_dep->next_table_field)
{
......@@ -1302,6 +1346,7 @@ void Table_value::now_bound(Func_dep_analyzer *fda,
}
}
/* Signal to outer join that one more table is known */
if (fda->outer_join_dep->unknown_args &&
!--fda->outer_join_dep->unknown_args)
{
......@@ -1318,6 +1363,7 @@ void Field_value::now_bound(Func_dep_analyzer *fda,
DBUG_PRINT("info", ("field %s.%s is now bound", field->table->alias,
field->field_name));
/* Signal to unique keys and expressions that use this field*/
for (Key_module *key_dep= table->keys; key_dep;
key_dep= key_dep->next_table_key)
{
......@@ -1337,8 +1383,8 @@ void Field_value::now_bound(Func_dep_analyzer *fda,
/*
Walk through expressions that depend on this field and 'notify' them
that this field is no longer unknown.
Walk through expressions that depend on this field and notify them
that this field is now known.
*/
void Field_value::signal_from_field_to_exprs(Func_dep_analyzer* fda,
Module_dep **bound_modules)
......@@ -1362,16 +1408,16 @@ bool Outer_join_module::now_bound(Func_dep_analyzer *fda,
Value_dep **bound_values)
{
DBUG_PRINT("info", ("Outer join eliminated"));
return TRUE; /* Signal to finish the process */
return TRUE; /* Signal out that the search is finished */
}
bool Equality_module::now_bound(Func_dep_analyzer *fda,
Value_dep **bound_values)
{
/* For field=expr and we got to know the expr, so we know the field */
if (mult_equal_fields)
{
/* It's a=b=c=... multiple equality. Mark all equality members as known. */
List_iterator<Field_value> it(*mult_equal_fields);
Field_value *fv;
while ((fv= it++))
......@@ -1387,6 +1433,7 @@ bool Equality_module::now_bound(Func_dep_analyzer *fda,
}
else
{
/* It's a fieldX=exprY equality. Mark exprY as known */
if (!field->bound)
{
/* Mark as bound and add to the list */
......@@ -1398,7 +1445,9 @@ bool Equality_module::now_bound(Func_dep_analyzer *fda,
return FALSE;
}
/* Unique key is known means its table is known */
bool Key_module::now_bound(Func_dep_analyzer *fda, Value_dep **bound_values)
{
if (!table->bound)
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7