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MDEV-238: SHOW EXPLAIN: Server crashes in JOIN::print_explain with FROM subquery and GROUP BY

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- Support SHOW EXPLAIN for selects that have "Using temporary; Using filesort".
This commit is contained in:
Sergey Petrunya
2012-05-10 13:43:48 +04:00
parent cdc9a1172d
commit 58b9164f04
6 changed files with 106 additions and 12 deletions
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25
mysql-test/r/show_explain.result
View File

@ -284,4 +284,29 @@ a
7
8
9
set debug='';
#
# MDEV-238: SHOW EXPLAIN: Server crashes in JOIN::print_explain with FROM subquery and GROUP BY
#
CREATE TABLE t2 ( a INT );
INSERT INTO t2 VALUES (1),(2),(1),(4),(2);
explain SELECT alias.a FROM t2, ( SELECT * FROM t2 ) AS alias GROUP BY alias.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 5 Using temporary; Using filesort
1 SIMPLE t2 ALL NULL NULL NULL NULL 5 Using join buffer (flat, BNL join)
set debug='d,show_explain_in_find_all_keys';
SELECT alias.a FROM t2, ( SELECT * FROM t2 ) AS alias GROUP BY alias.a;
# NOTE: current code will not show "Using join buffer":
show explain for $thr2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 5 Using temporary; Using filesort
1 SIMPLE t2 ALL NULL NULL NULL NULL 5
Warnings:
Note 1003 SELECT alias.a FROM t2, ( SELECT * FROM t2 ) AS alias GROUP BY alias.a
a
1
2
4
set debug='';
DROP TABLE t2;
drop table t0,t1;

22
mysql-test/t/show_explain.test
View File

@ -300,8 +300,30 @@ connection default;
evalp show explain for $thr2;
connection con1;
reap;
set debug='';
--echo #
--echo # MDEV-238: SHOW EXPLAIN: Server crashes in JOIN::print_explain with FROM subquery and GROUP BY
--echo #
CREATE TABLE t2 ( a INT );
INSERT INTO t2 VALUES (1),(2),(1),(4),(2);
explain SELECT alias.a FROM t2, ( SELECT * FROM t2 ) AS alias GROUP BY alias.a;
set debug='d,show_explain_in_find_all_keys';
send SELECT alias.a FROM t2, ( SELECT * FROM t2 ) AS alias GROUP BY alias.a;
connection default;
--source include/wait_condition.inc
--echo # NOTE: current code will not show "Using join buffer":
evalp show explain for $thr2;
connection con1;
reap;
set debug='';
## TODO: Test this: have several SHOW EXPLAIN requests be queued up for a
## thread and served together.
DROP TABLE t2;
drop table t0,t1;

6
sql/filesort.cc
View File

@ -515,6 +515,12 @@ static ha_rows find_all_keys(SORTPARAM *param, SQL_SELECT *select,
if (indexfile || flag)
ref_pos= &file->ref[0];
next_pos=ref_pos;
DBUG_EXECUTE_IF("show_explain_in_find_all_keys",
dbug_serve_apcs(thd, 1);
);
if (! indexfile && ! quick_select)
{
next_pos=(uchar*) 0; /* Find records in sequence */

44
sql/sql_select.cc
View File

@ -7132,28 +7132,36 @@ prev_record_reads(POSITION *positions, uint idx, table_map found_ref)
return found;
}
enum enum_exec_or_opt {WALK_OPTIMIZATION_TABS , WALK_EXECUTION_TABS};
/*
Enumerate join tabs in breadth-first fashion, including const tables.
*/
JOIN_TAB *first_breadth_first_tab(JOIN *join)
JOIN_TAB *first_breadth_first_tab(JOIN *join, enum enum_exec_or_opt tabs_kind)
{
return join->join_tab; /* There's always one (i.e. first) table */
/* There's always one (i.e. first) table */
return (tabs_kind == WALK_EXECUTION_TABS)? join->join_tab:
join->table_access_tabs;
}
JOIN_TAB *next_breadth_first_tab(JOIN *join, JOIN_TAB *tab)
JOIN_TAB *next_breadth_first_tab(JOIN *join, enum enum_exec_or_opt tabs_kind,
JOIN_TAB *tab)
{
JOIN_TAB* const first_top_tab= first_breadth_first_tab(join, tabs_kind);
const uint n_top_tabs_count= (tabs_kind == WALK_EXECUTION_TABS)?
join->top_join_tab_count:
join->top_table_access_tabs_count;
if (!tab->bush_root_tab)
{
/* We're at top level. Get the next top-level tab */
tab++;
if (tab < join->join_tab + join->top_join_tab_count)
if (tab < first_top_tab + n_top_tabs_count)
return tab;
/* No more top-level tabs. Switch to enumerating SJM nest children */
tab= join->join_tab;
tab= first_top_tab;
}
else
{
@ -7177,7 +7185,7 @@ JOIN_TAB *next_breadth_first_tab(JOIN *join, JOIN_TAB *tab)
Ok, "tab" points to a top-level table, and we need to find the next SJM
nest and enter it.
*/
for (; tab < join->join_tab + join->top_join_tab_count; tab++)
for (; tab < first_top_tab + n_top_tabs_count; tab++)
{
if (tab->bush_children)
return tab->bush_children->start;
@ -7201,7 +7209,7 @@ JOIN_TAB *first_top_level_tab(JOIN *join, enum enum_with_const_tables with_const
JOIN_TAB *next_top_level_tab(JOIN *join, JOIN_TAB *tab)
{
tab= next_breadth_first_tab(join, tab);
tab= next_breadth_first_tab(join, WALK_EXECUTION_TABS, tab);
if (tab && tab->bush_root_tab)
tab= NULL;
return tab;
@ -7501,6 +7509,13 @@ get_best_combination(JOIN *join)
join->top_join_tab_count= join->join_tab_ranges.head()->end -
join->join_tab_ranges.head()->start;
/*
Save pointers to select join tabs for SHOW EXPLAIN
*/
join->table_access_tabs= join->join_tab;
join->top_table_access_tabs_count= join->top_join_tab_count;
update_depend_map(join);
DBUG_RETURN(0);
}
@ -7922,6 +7937,7 @@ JOIN::make_simple_join(JOIN *parent, TABLE *temp_table)
!(parent->join_tab_reexec= (JOIN_TAB*) thd->alloc(sizeof(JOIN_TAB))))
DBUG_RETURN(TRUE); /* purecov: inspected */
// psergey-todo: here, save the pointer for original join_tabs.
join_tab= parent->join_tab_reexec;
table= &parent->table_reexec[0]; parent->table_reexec[0]= temp_table;
table_count= top_join_tab_count= 1;
@ -10077,7 +10093,12 @@ void JOIN_TAB::cleanup()
if (cache)
{
cache->free();
cache= 0;
cache= 0; // psergey: this is why we don't see "Using join cache" in SHOW EXPLAIN
// when it is run for "Using temporary+filesort" queries while they
// are at reading-from-tmp-table phase.
//
// TODO ask igor if this can be just moved to later phase
// (JOIN_CACHE objects themselves are not big, arent they)
}
limit= 0;
if (table)
@ -21204,9 +21225,10 @@ int JOIN::print_explain(select_result_sink *result, bool on_the_fly,
bool printing_materialize_nest= FALSE;
uint select_id= join->select_lex->select_number;
JOIN_TAB* const first_top_tab= first_breadth_first_tab(join, WALK_OPTIMIZATION_TABS);
for (JOIN_TAB *tab= first_breadth_first_tab(join); tab;
tab= next_breadth_first_tab(join, tab))
for (JOIN_TAB *tab= first_breadth_first_tab(join, WALK_OPTIMIZATION_TABS); tab;
tab= next_breadth_first_tab(join, WALK_OPTIMIZATION_TABS, tab))
{
if (tab->bush_root_tab)
{
@ -21643,7 +21665,7 @@ int JOIN::print_explain(select_result_sink *result, bool on_the_fly,
extra.append(STRING_WITH_LEN("; End temporary"));
else if (tab->do_firstmatch)
{
if (tab->do_firstmatch == join->join_tab - 1)
if (tab->do_firstmatch == /*join->join_tab*/ first_top_tab - 1)
extra.append(STRING_WITH_LEN("; FirstMatch"));
else
{

14
sql/sql_select.h
View File

@ -896,6 +896,20 @@ protected:
public:
JOIN_TAB *join_tab, **best_ref;
/*
For "Using temporary+Using filesort" queries, JOIN::join_tab can point to
either:
1. array of join tabs describing how to run the select, or
2. array of single join tab describing read from the temporary table.
SHOW EXPLAIN code needs to read/show #1. This is why two next members are
there for saving it.
*/
JOIN_TAB *table_access_tabs;
uint top_table_access_tabs_count;
JOIN_TAB **map2table; ///< mapping between table indexes and JOIN_TABs
JOIN_TAB *join_tab_save; ///< saved join_tab for subquery reexecution

7
sql/table.h
View File

@ -850,7 +850,12 @@ struct st_table {
See TABLE_LIST::process_index_hints().
*/
bool force_index_group;
bool distinct,const_table,no_rows, used_for_duplicate_elimination;
/*
TRUE<=> this table was created with create_tmp_table(... distinct=TRUE..)
call
*/
bool distinct;
bool const_table,no_rows, used_for_duplicate_elimination;
/**
If set, the optimizer has found that row retrieval should access index