Commit 24c2fea6 authored by Sergey Petrunya's avatar Sergey Petrunya

MWL#17: Table elimination

- Address review feedback R4: better comments, formatting
parent d762bf21
...@@ -290,10 +290,6 @@ print "time for select_one_attribute ($count:$rows): " . ...@@ -290,10 +290,6 @@ print "time for select_one_attribute ($count:$rows): " .
timestr(timediff($end_time, $loop_time),"all") . "\n"; timestr(timediff($end_time, $loop_time),"all") . "\n";
###
### TODO...
###
; ;
#### ####
......
...@@ -24,8 +24,10 @@ ...@@ -24,8 +24,10 @@
elimination is as follows: suppose we have a left join elimination is as follows: suppose we have a left join
SELECT * FROM t1 LEFT JOIN SELECT * FROM t1 LEFT JOIN
(t2 JOIN t3) ON t3.primary_key=t1.col AND (t2 JOIN t3) ON t2.primary_key=t1.col AND
t4.primary_key=t2.col t2.primary_key=t2.col
WHERE ...
such that such that
* columns of the inner tables are not used anywhere ouside the outer join * columns of the inner tables are not used anywhere ouside the outer join
(not in WHERE, not in GROUP/ORDER BY clause, not in select list etc etc), (not in WHERE, not in GROUP/ORDER BY clause, not in select list etc etc),
...@@ -41,11 +43,11 @@ ...@@ -41,11 +43,11 @@
MODULE INTERFACE MODULE INTERFACE
================ ================
The module has one entry point - eliminate_tables() function, which one The module has one entry point - the eliminate_tables() function, which one
needs to call (once) at some point before the join optimization. needs to call (once) at some point before join optimization.
eliminate_tables() operates over the JOIN structures. Logically, it eliminate_tables() operates over the JOIN structures. Logically, it
removes the right sides of outer join nests. Physically, it changes the removes the inner tables of an outer join operation together with the
following members: operation itself. Physically, it changes the following members:
* Eliminated tables are marked as constant and moved to the front of the * Eliminated tables are marked as constant and moved to the front of the
join order. join order.
...@@ -119,13 +121,14 @@ ...@@ -119,13 +121,14 @@
= No outgoing edges. Once we reach it, we know we can eliminate the = No outgoing edges. Once we reach it, we know we can eliminate the
outer join. outer join.
A module may depend on multiple values, and hence its primary attribute is A module may depend on multiple values, and hence its primary attribute is
the number of its depedencies that are not bound. the number of its arguments that are not bound.
The algorithm starts with equality nodes that don't have any incoming edges The algorithm starts with equality nodes that don't have any incoming edges
(their expressions are either constant or depend only on tables that are (their expressions are either constant or depend only on tables that are
outside of the outer join in question) and performns a breadth-first 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 traversal. If we reach the outer join nest node, it means outer join is
functionally dependent and can be eliminated. Otherwise it cannot be. functionally dependent and can be eliminated. Otherwise it cannot be
eliminated.
HANDLING MULTIPLE NESTED OUTER JOINS HANDLING MULTIPLE NESTED OUTER JOINS
==================================== ====================================
...@@ -230,8 +233,9 @@ class Dep_value_field : public Dep_value ...@@ -230,8 +233,9 @@ class Dep_value_field : public Dep_value
Field *field; /* Field this object is representing */ Field *field; /* Field this object is representing */
/* Iteration over unbound modules that are our dependencies */ /* Iteration over unbound modules that are our dependencies */
virtual Iterator init_unbound_modules_iter(char *buf); Iterator init_unbound_modules_iter(char *buf);
virtual Dep_module* get_next_unbound_module(Dep_analysis_context *dac, Iterator iter); Dep_module* get_next_unbound_module(Dep_analysis_context *dac,
Iterator iter);
void make_unbound_modules_iter_skip_keys(Iterator iter); void make_unbound_modules_iter_skip_keys(Iterator iter);
...@@ -269,9 +273,11 @@ const size_t Dep_value_field::iterator_size= ...@@ -269,9 +273,11 @@ const size_t Dep_value_field::iterator_size=
/* /*
A table value. There is one Dep_value_table object for every table that can A table value. There is one Dep_value_table object for every table that can
potentially be eliminated. potentially be eliminated.
Dependencies:
- table depends on any of its unique keys Table becomes bound as soon as some of its unique keys becomes bound
- has its fields and embedding outer join as dependency Once the table is bound:
- all of its fields are bound
- its embedding outer join has one less unknown argument
*/ */
class Dep_value_table : public Dep_value class Dep_value_table : public Dep_value
...@@ -280,14 +286,15 @@ class Dep_value_table : public Dep_value ...@@ -280,14 +286,15 @@ class Dep_value_table : public Dep_value
Dep_value_table(TABLE *table_arg) : Dep_value_table(TABLE *table_arg) :
table(table_arg), fields(NULL), keys(NULL) table(table_arg), fields(NULL), keys(NULL)
{} {}
TABLE *table; TABLE *table; /* Table this object is representing */
Dep_value_field *fields; /* Ordered list of fields that belong to this table */ /* Ordered list of fields that belong to this table */
Dep_value_field *fields;
Dep_module_key *keys; /* Ordered list of Unique keys in this table */ Dep_module_key *keys; /* Ordered list of Unique keys in this table */
/* Iteration over unbound modules that are our dependencies */ /* Iteration over unbound modules that are our dependencies */
Iterator init_unbound_modules_iter(char *buf); Iterator init_unbound_modules_iter(char *buf);
Dep_module* get_next_unbound_module(Dep_analysis_context *dac, Iterator iter); Dep_module* get_next_unbound_module(Dep_analysis_context *dac,
Iterator iter);
static const size_t iterator_size; static const size_t iterator_size;
private: private:
class Module_iter class Module_iter
...@@ -295,7 +302,7 @@ class Dep_value_table : public Dep_value ...@@ -295,7 +302,7 @@ class Dep_value_table : public Dep_value
public: public:
/* Space for field iterator */ /* Space for field iterator */
char buf[Dep_value_field::iterator_size]; char buf[Dep_value_field::iterator_size];
/* !NULL <=> iterating over dependenant modules of this field */ /* !NULL <=> iterating over depdenent modules of this field */
Dep_value_field *field_dep; Dep_value_field *field_dep;
bool returned_goal; bool returned_goal;
}; };
...@@ -339,7 +346,8 @@ class Dep_module : public Sql_alloc ...@@ -339,7 +346,8 @@ class Dep_module : public Sql_alloc
/* Iteration over values that */ /* Iteration over values that */
typedef char *Iterator; typedef char *Iterator;
virtual Iterator init_unbound_values_iter(char *buf)=0; virtual Iterator init_unbound_values_iter(char *buf)=0;
virtual Dep_value* get_next_unbound_value(Dep_analysis_context *dac, Iterator iter)=0; virtual Dep_value* get_next_unbound_value(Dep_analysis_context *dac,
Iterator iter)=0;
static const size_t iterator_size; static const size_t iterator_size;
protected: protected:
uint unbound_args; uint unbound_args;
...@@ -385,9 +393,9 @@ const size_t Dep_module_expr::iterator_size= ...@@ -385,9 +393,9 @@ const size_t Dep_module_expr::iterator_size=
/* /*
A Unique key A Unique key module
- Unique key depends on all of its components - Unique key has all of its components as arguments
- Key's table is its dependency - Once unique key is bound, its table value is known
*/ */
class Dep_module_key: public Dep_module class Dep_module_key: public Dep_module
...@@ -539,8 +547,8 @@ void add_module_expr(Dep_analysis_context *dac, Dep_module_expr **eq_mod, ...@@ -539,8 +547,8 @@ void add_module_expr(Dep_analysis_context *dac, Dep_module_expr **eq_mod,
The idea behind table elimination is that if we have an outer join: The idea behind table elimination is that if we have an outer join:
SELECT * FROM t1 LEFT JOIN SELECT * FROM t1 LEFT JOIN
(t2 JOIN t3) ON t3.primary_key=t1.col AND (t2 JOIN t3) ON t2.primary_key=t1.col AND
t4.primary_key=t2.col t3.primary_key=t2.col
such that such that
1. columns of the inner tables are not used anywhere ouside the outer 1. columns of the inner tables are not used anywhere ouside the outer
...@@ -559,8 +567,8 @@ void add_module_expr(Dep_analysis_context *dac, Dep_module_expr **eq_mod, ...@@ -559,8 +567,8 @@ void add_module_expr(Dep_analysis_context *dac, Dep_module_expr **eq_mod,
tables that are not used in select list/GROUP BY/ORDER BY/HAVING/etc and tables that are not used in select list/GROUP BY/ORDER BY/HAVING/etc and
thus can possibly be eliminated. thus can possibly be eliminated.
After this, if #1 is met, the function calls eliminate_tables_for_list() After this, if #1 is met, the function calls eliminate_tables_for_list()
that checks #2. that checks #2.
SIDE EFFECTS SIDE EFFECTS
See the OVERVIEW section at the top of this file. See the OVERVIEW section at the top of this file.
...@@ -656,7 +664,14 @@ void eliminate_tables(JOIN *join) ...@@ -656,7 +664,14 @@ void eliminate_tables(JOIN *join)
select list, HAVING, other ON expressions, etc). select list, HAVING, other ON expressions, etc).
DESCRIPTION DESCRIPTION
Perform table elimination in a given join list. Perform table elimination in a given join list:
- First, walk through join list members and try doing table elimination for
them.
- Then, if the join list itself is an inner side of outer join
(on_expr!=NULL), then try to eliminate the entire join list.
See "HANDLING MULTIPLE NESTED OUTER JOINS" section at the top of this file
for more detailed description and justification.
RETURN RETURN
TRUE The entire join list eliminated TRUE The entire join list eliminated
...@@ -1677,7 +1692,8 @@ Dep_value::Iterator Dep_value_field::init_unbound_modules_iter(char *buf) ...@@ -1677,7 +1692,8 @@ Dep_value::Iterator Dep_value_field::init_unbound_modules_iter(char *buf)
} }
void Dep_value_field::make_unbound_modules_iter_skip_keys(Dep_value::Iterator iter) void
Dep_value_field::make_unbound_modules_iter_skip_keys(Dep_value::Iterator iter)
{ {
((Module_iter*)iter)->key_dep= NULL; ((Module_iter*)iter)->key_dep= NULL;
} }
......
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