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EXPLAIN FORMAT=JSON

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Add support for semi-join strategies: FirstMatch, DuplicateWeedout,
LooseScan.
This commit is contained in:
Sergei Petrunia
2014-12-02 01:40:10 +03:00
parent a35b05399e
commit 0000695025
5 changed files with 123 additions and 3 deletions
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72
mysql-test/r/explain_json.result
View File

@ -592,5 +592,77 @@ EXPLAIN
}
}
}
#
# First-Match
#
explain
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t2 ALL NULL NULL NULL NULL 10
1 PRIMARY t1 ALL NULL NULL NULL NULL 10 Using where; FirstMatch(t2); Using join buffer (flat, BNL join)
explain format=json
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "t2",
"access_type": "ALL",
"rows": 10,
"filtered": 100
},
"block-nl-join": {
"table": {
"table_name": "t1",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"first_match": "t2"
},
"buffer_type": "flat",
"join_type": "BNL",
"attached_condition": "((t1.b = t2.b) and (t1.a = t2.a))"
}
}
}
#
# Duplicate Weedout
#
set @tmp= @@optimizer_switch;
set optimizer_switch='firstmatch=off';
explain
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t2 ALL NULL NULL NULL NULL 10
1 PRIMARY t1 ALL NULL NULL NULL NULL 10 Using where; Start temporary; End temporary; Using join buffer (flat, BNL join)
explain format=json
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "t2",
"access_type": "ALL",
"rows": 10,
"filtered": 100
},
"duplicates_removal": {
"block-nl-join": {
"table": {
"table_name": "t1",
"access_type": "ALL",
"rows": 10,
"filtered": 100
},
"buffer_type": "flat",
"join_type": "BNL",
"attached_condition": "((t1.b = t2.b) and (t1.a = t2.a))"
}
}
}
}
set optimizer_switch=@tmp;
drop table t1,t2;
drop table t0;

19
mysql-test/t/explain_json.test
View File

@ -114,6 +114,25 @@ insert into t2 select * from t1;
explain format=json
select * from t1,t2 where t1.a in ( select a from t0);
--echo #
--echo # First-Match
--echo #
explain
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
explain format=json
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
--echo #
--echo # Duplicate Weedout
--echo #
set @tmp= @@optimizer_switch;
set optimizer_switch='firstmatch=off';
explain
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
explain format=json
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
set optimizer_switch=@tmp;
drop table t1,t2;
drop table t0;

21
sql/sql_explain.cc
View File

@ -732,7 +732,13 @@ void Explain_basic_join::print_explain_json(Explain_query *query,
writer->add_member("select_id").add_ll(select_id);
for (uint i=0; i< n_join_tabs; i++)
{
if (join_tabs[i]->start_dups_weedout)
writer->add_member("duplicates_removal").start_object();
join_tabs[i]->print_explain_json(query, writer, is_analyze);
if (join_tabs[i]->end_dups_weedout)
writer->end_object();
}
print_explain_json_for_children(query, writer, is_analyze);
writer->end_object();
@ -1089,9 +1095,7 @@ void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_t
write_item(writer, pushed_index_cond);
break;
case ET_USING_WHERE:
if (where_cond)
{
writer->add_member("attached_condition");
/*
We are printing the condition that is checked when scanning this
table.
@ -1099,8 +1103,12 @@ void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_t
- in other cases, it is where_cond.
*/
Item *item= bka_type.is_using_jbuf()? cache_cond: where_cond;
if (item)
{
writer->add_member("attached_condition");
write_item(writer, item);
}
}
break;
case ET_USING_INDEX:
writer->add_member("using_index").add_bool(true);
@ -1110,6 +1118,15 @@ void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_t
break;
case ET_USING_JOIN_BUFFER:
/* Do nothing. Join buffer is handled differently */
case ET_START_TEMPORARY:
case ET_END_TEMPORARY:
/* Handled as "duplicates_removal: { ... } */
break;
case ET_FIRST_MATCH:
writer->add_member("first_match").add_str(firstmatch_table_name.c_ptr());
break;
case ET_LOOSESCAN:
writer->add_member("loose_scan").add_bool(true);
break;
default:
DBUG_ASSERT(0);

5
sql/sql_explain.h
View File

@ -539,6 +539,8 @@ public:
Explain_table_access() :
derived_select_number(0),
non_merged_sjm_number(0),
start_dups_weedout(false),
end_dups_weedout(false),
where_cond(NULL),
cache_cond(NULL),
pushed_index_cond(NULL),
@ -616,6 +618,9 @@ public:
StringBuffer<32> firstmatch_table_name;
bool start_dups_weedout;
bool end_dups_weedout;
/*
Note: lifespan of WHERE condition is less than lifespan of this object.
The below two are valid if tags include "ET_USING_WHERE".

7
sql/sql_select.cc
View File

@ -23641,9 +23641,16 @@ void JOIN_TAB::save_explain_data(Explain_table_access *eta, table_map prefix_tab
}
if (tab->first_weedout_table)
{
eta->start_dups_weedout= true;
eta->push_extra(ET_START_TEMPORARY);
}
if (tab->check_weed_out_table)
{
eta->push_extra(ET_END_TEMPORARY);
eta->end_dups_weedout= true;
}
else if (tab->do_firstmatch)
{
if (tab->do_firstmatch == /*join->join_tab*/ first_top_tab - 1)