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EXPLAIN FORMAT=JSON: further development

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Writing JSON:
- Fix a bug in Single_line_formatting_helper
- Add Json_writer_nesting_guard - safety class

EXPLAIN JSON support
- Add basic subquery support
- Add tests for UNION/UNION ALL.
This commit is contained in:
Sergei Petrunia
2014-11-27 19:32:48 +03:00
parent 3d5f97fd70
commit 37c444e1a0
9 changed files with 298 additions and 14 deletions
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134
mysql-test/r/explain_json.result
View File

@ -175,4 +175,138 @@ EXPLAIN
}
}
drop table t1,t2;
#
# Try a UNION
#
explain format=json select * from t0 A union select * from t0 B;
EXPLAIN
{
"query_block": {
"union_result": {
"table_name": "<union1,2>",
"access_type": "ALL",
"query_specifications": [
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "A",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
},
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "B",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
}
]
}
}
}
explain format=json select * from t0 A union all select * from t0 B;
EXPLAIN
{
"query_block": {
"union_result": {
"table_name": "<union1,2>",
"access_type": "ALL",
"query_specifications": [
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "A",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
},
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "B",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
}
]
}
}
}
#
# Subqueries
#
create table t1 (a int, b int);
insert into t1 select a,a from t0;
explain format=json select a, a > (select max(b) from t1 where t1.b=t0.a) from t0;
EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100
},
"subqueries": [
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "t1",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "(t1.b = t0.a)"
}
}
}
]
}
}
explain format=json
select * from t0 where
a > (select max(b) from t1 where t1.b=t0.a) or a < 3 ;
EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "((t0.a > (subquery#2)) or (t0.a < 3))"
},
"subqueries": [
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "t1",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "(t1.b = t0.a)"
}
}
}
]
}
}
drop table t1;
drop table t0;

20
mysql-test/t/explain_json.test
View File

@ -39,4 +39,24 @@ explain format=json select * from t2 where a1=1 or (b1=2 and b2=3);
explain format=json select * from t0,t2 where t2.b1=t0.a and t2.b2=4;
drop table t1,t2;
--echo #
--echo # Try a UNION
--echo #
explain format=json select * from t0 A union select * from t0 B;
explain format=json select * from t0 A union all select * from t0 B;
--echo #
--echo # Subqueries
--echo #
create table t1 (a int, b int);
insert into t1 select a,a from t0;
explain format=json select a, a > (select max(b) from t1 where t1.b=t0.a) from t0;
explain format=json
select * from t0 where
a > (select max(b) from t1 where t1.b=t0.a) or a < 3 ;
drop table t1;
drop table t0;

7
sql/item.cc
View File

@ -7536,6 +7536,13 @@ void Item_cache_wrapper::init_on_demand()
void Item_cache_wrapper::print(String *str, enum_query_type query_type)
{
if (query_type == QT_EXPLAIN)
{
/* Don't print the cache in EXPLAIN EXTENDED */
orig_item->print(str, query_type);
return;
}
str->append(func_name());
if (expr_cache)
{

19
sql/item_subselect.cc
View File

@ -894,6 +894,21 @@ void Item_subselect::update_used_tables()
void Item_subselect::print(String *str, enum_query_type query_type)
{
if (query_type == QT_EXPLAIN)
{
str->append("(subquery#");
if (engine)
{
char buf[64];
ll2str(engine->get_identifier(), buf, 10, 0);
str->append(buf);
}
else
str->append("NULL"); // TODO: what exactly does this mean?
str->append(")");
return;
}
if (engine)
{
str->append('(');
@ -3716,6 +3731,10 @@ int subselect_union_engine::exec()
return res;
}
int subselect_union_engine::get_identifier()
{
return unit->first_select()->select_number;
}
/*
Search for at least one row satisfying select condition

1
sql/item_subselect.h
View File

@ -871,6 +871,7 @@ public:
bool is_executed() const;
bool no_rows();
virtual enum_engine_type engine_type() { return UNION_ENGINE; }
int get_identifier();
};

24
sql/my_json_writer.cc
View File

@ -79,7 +79,12 @@ Json_writer& Json_writer::add_member(const char *name)
return *this;
}
/* Used by formatting helper to print something that is formatted by the helper. */
/*
Used by formatting helper to print something that is formatted by the helper.
We should only separate it from the previous element.
*/
void Json_writer::start_sub_element()
{
//element_started= true;
@ -184,6 +189,7 @@ bool Single_line_formatting_helper::on_add_member(const char *name)
return false; // not handled
}
bool Single_line_formatting_helper::on_start_array()
{
if (state == ADD_MEMBER)
@ -200,6 +206,7 @@ bool Single_line_formatting_helper::on_start_array()
}
}
bool Single_line_formatting_helper::on_end_array()
{
if (state == IN_ARRAY)
@ -211,12 +218,14 @@ bool Single_line_formatting_helper::on_end_array()
return false; // not handled
}
void Single_line_formatting_helper::on_start_object()
{
// Nested objects will not be printed on one line
disable_and_flush();
}
bool Single_line_formatting_helper::on_add_str(const char *str)
{
if (state == IN_ARRAY)
@ -244,9 +253,13 @@ bool Single_line_formatting_helper::on_add_str(const char *str)
return false; // not handled
}
/*
Append everything accumulated to the output on one line
*/
void Single_line_formatting_helper::flush_on_one_line()
{
// append everything to output on one line
owner->start_sub_element();
char *ptr= buffer;
int nr= 0;
@ -281,6 +294,7 @@ void Single_line_formatting_helper::flush_on_one_line()
void Single_line_formatting_helper::disable_and_flush()
{
bool start_array= (state == IN_ARRAY);
state= DISABLED;
// deactivate ourselves and flush all accumulated calls.
char *ptr= buffer;
@ -291,11 +305,13 @@ void Single_line_formatting_helper::disable_and_flush()
if (nr == 0)
{
owner->add_member(str);
if (start_array)
owner->start_array();
}
else
{
if (nr == 1)
owner->start_array();
//if (nr == 1)
// owner->start_array();
owner->add_str(str);
}

59
sql/my_json_writer.h
View File

@ -34,9 +34,30 @@ class Single_line_formatting_helper
DISABLED
};
/*
This works like a finite automaton.
state=DISABLED means the helper is disabled - all on_XXX functions will
return false (which means "not handled") and do nothing.
+->-+
| v
INACTIVE ---> ADD_MEMBER ---> IN_ARRAY--->-+
^ |
+------------------<--------------------+
For other states:
INACTIVE - initial state, we have nothing.
ADD_MEMBER - add_member() was called, the buffer has "member_name\0".
IN_ARRAY - start_array() was called.
*/
enum enum_state state;
enum { MAX_LINE_LEN= 80 };
char buffer[80];
/* The data in the buffer is located between buffer[0] and buf_ptr */
char *buf_ptr;
uint line_len;
@ -101,6 +122,7 @@ private:
enum { INDENT_SIZE = 2 };
friend class Single_line_formatting_helper;
friend class Json_writer_nesting_guard;
bool document_start;
bool element_started;
bool first_child;
@ -116,3 +138,40 @@ public:
String output;
};
/*
RAII-based helper class to detect incorrect use of Json_writer.
The idea is that a function typically must leave Json_writer at the same
identation level as it was when it was invoked. Leaving it at a different
level typically means we forgot to close an object or an array
So, here is a way to guard
void foo(Json_writer *writer)
{
Json_writer_nesting_guard(writer);
.. do something with writer
// at the end of the function, ~Json_writer_nesting_guard() is called
// and it makes sure that the nesting is the same as when the function was
// entered.
}
*/
class Json_writer_nesting_guard
{
Json_writer* writer;
int indent_level;
public:
Json_writer_nesting_guard(Json_writer *writer_arg) :
writer(writer_arg),
indent_level(writer->indent_level)
{}
~Json_writer_nesting_guard()
{
DBUG_ASSERT(indent_level == writer->indent_level);
}
};

38
sql/sql_explain.cc
View File

@ -303,7 +303,7 @@ int Explain_union::print_explain(Explain_query *query,
uint8 explain_flags,
bool is_analyze)
{
const CHARSET_INFO *cs= system_charset_info;
//const CHARSET_INFO *cs= system_charset_info;
char table_name_buffer[SAFE_NAME_LEN];
/* print all UNION children, in order */
@ -391,6 +391,7 @@ int Explain_union::print_explain(Explain_query *query,
void Explain_union::print_explain_json(Explain_query *query,
Json_writer *writer, bool is_analyze)
{
Json_writer_nesting_guard guard(writer);
char table_name_buffer[SAFE_NAME_LEN];
writer->add_member("query_block").start_object();
@ -404,17 +405,18 @@ void Explain_union::print_explain_json(Explain_query *query,
for (int i= 0; i < (int) union_members.elements(); i++)
{
writer->start_object();
writer->add_member("dependent").add_str("TODO");
writer->add_member("cacheable").add_str("TODO");
//writer->add_member("dependent").add_str("TODO");
//writer->add_member("cacheable").add_str("TODO");
Explain_select *sel= query->get_select(union_members.at(i));
sel->print_explain_json(query, writer, is_analyze);
writer->end_object();
}
writer->end_array();
//TODO: print_explain_for_children
print_explain_json_for_children(query, writer, is_analyze);
writer->end_object();
writer->end_object(); // union_result
writer->end_object(); // query_block
}
@ -437,6 +439,25 @@ int Explain_node::print_explain_for_children(Explain_query *query,
}
void Explain_node::print_explain_json_for_children(Explain_query *query,
Json_writer *writer,
bool is_analyze)
{
if (!children.elements())
return;
writer->add_member("subqueries").start_array();
for (int i= 0; i < (int) children.elements(); i++)
{
writer->start_object();
Explain_node *node= query->get_node(children.at(i));
node->print_explain_json(query, writer, is_analyze);
writer->end_object();
}
writer->end_array();
}
void Explain_select::replace_table(uint idx, Explain_table_access *new_tab)
{
delete join_tabs[idx];
@ -514,6 +535,8 @@ int Explain_select::print_explain(Explain_query *query,
void Explain_select::print_explain_json(Explain_query *query,
Json_writer *writer, bool is_analyze)
{
Json_writer_nesting_guard guard(writer);
writer->add_member("query_block").start_object();
writer->add_member("select_id").add_ll(1);
if (message)
@ -530,6 +553,8 @@ void Explain_select::print_explain_json(Explain_query *query,
join_tabs[i]->print_explain_json(writer, is_analyze);
}
}
print_explain_json_for_children(query, writer, is_analyze);
writer->end_object();
}
@ -658,7 +683,7 @@ int Explain_table_access::print_explain(select_result_sink *output, uint8 explai
uint select_id, const char *select_type,
bool using_temporary, bool using_filesort)
{
const CHARSET_INFO *cs= system_charset_info;
//const CHARSET_INFO *cs= system_charset_info;
List<Item> item_list;
Item *item_null= new Item_null();
@ -899,6 +924,7 @@ void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_t
void Explain_table_access::print_explain_json(Json_writer *writer,
bool is_analyze)
{
Json_writer_nesting_guard guard(writer);
writer->add_member("table").start_object();
writer->add_member("table_name").add_str(table_name);

2
sql/sql_explain.h
View File

@ -112,6 +112,8 @@ public:
int print_explain_for_children(Explain_query *query, select_result_sink *output,
uint8 explain_flags, bool is_analyze);
void print_explain_json_for_children(Explain_query *query,
Json_writer *writer, bool is_analyze);
virtual ~Explain_node(){}
};