Mysql Advanced - パフォーマンス分析ツール (2)

6. クエリステートメントを分析します: EXPLAIN

6.1 基本的な構文

EXPLAIN または DESCRIBE ステートメントの構文は次のとおりです。

EXPLAIN SELECT select_options
或者
DESCRIBE SELECT select_options

特定のクエリの実行プランを確認したい場合は、次のように特定のクエリステートメントの前に EXPLAIN を追加します。

mysql> EXPLAIN SELECT 1;

EXPLAIN文で出力される各列の機能は以下のとおりです。

ここに画像の説明を挿入します

6.2 データの準備

CREATE TABLE s1 (
	id INT AUTO_INCREMENT,
	key1 VARCHAR ( 100 ),
	key2 INT,
	key3 VARCHAR ( 100 ),
	key_part1 VARCHAR ( 100 ),
	key_part2 VARCHAR ( 100 ),
	key_part3 VARCHAR ( 100 ),
	common_field VARCHAR ( 100 ),
	PRIMARY KEY ( id ),
	INDEX idx_key1 ( key1 ),
	UNIQUE INDEX idx_key2 ( key2 ),
	INDEX idx_key3 ( key3 ),
	INDEX idx_key_part ( key_part1, key_part2, key_part3 ) 
) ENGINE = INNODB CHARSET = utf8;
CREATE TABLE s2 (
	id INT AUTO_INCREMENT,
	key1 VARCHAR ( 100 ),
	key2 INT,
	key3 VARCHAR ( 100 ),
	key_part1 VARCHAR ( 100 ),
	key_part2 VARCHAR ( 100 ),
	key_part3 VARCHAR ( 100 ),
	common_field VARCHAR ( 100 ),
	PRIMARY KEY ( id ),
	INDEX idx_key1 ( key1 ),
	UNIQUE INDEX idx_key2 ( key2 ),
	INDEX idx_key3 ( key3 ),
INDEX idx_key_part ( key_part1, key_part2, key_part3 ) 
) ENGINE = INNODB CHARSET = utf8;

パラメータ log_bin_trust_function_creators を設定します

関数を作成します。エラーが報告された場合は、次のコマンドを有効にする必要があります: 関数設定の作成を許可:

set global log_bin_trust_function_creators=1; # 不加global只是当前窗口有效。

関数の作成

DELIMITER //
CREATE FUNCTION rand_string1 ( n INT ) RETURNS VARCHAR ( 255 ) #该函数会返回一个字符串
BEGIN
	DECLARE
		chars_str VARCHAR ( 100 ) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFJHIJKLMNOPQRSTUVWXYZ';
	DECLARE
		return_str VARCHAR ( 255 ) DEFAULT '';
	DECLARE
		i INT DEFAULT 0;
	WHILE
			i < n DO
			
			SET return_str = CONCAT(
				return_str,
			SUBSTRING( chars_str, FLOOR( 1+RAND ()* 52 ), 1 ));
		
		SET i = i + 1;
		
	END WHILE;
	RETURN return_str;
	
END // 
DELIMITER;

ストアドプロシージャを作成する

s1 テーブルにデータを挿入するストアドプロシージャを作成します。

DELIMITER //
CREATE PROCEDURE insert_s1 (
	IN min_num INT ( 10 ),
	IN max_num INT ( 10 )) BEGIN
	DECLARE
		i INT DEFAULT 0;
	
	SET autocommit = 0;
	REPEAT
			
			SET i = i + 1;
		INSERT INTO s1
		VALUES
			(
				( min_num + i ),
				rand_string1 ( 6 ),
				( min_num + 30 * i + 5 ),
				rand_string1 ( 6 ),
				rand_string1 ( 10 ),
				rand_string1 ( 5 ),
				rand_string1 ( 10 ),
			rand_string1 ( 10 ));
		UNTIL i = max_num 
	END REPEAT;
	COMMIT;
	
END // 
DELIMITER;

s2 テーブルにデータを挿入するストアドプロシージャを作成します。

DELIMITER //
CREATE PROCEDURE insert_s2 (
	IN min_num INT ( 10 ),
	IN max_num INT ( 10 )) BEGIN
	DECLARE
		i INT DEFAULT 0;
	
	SET autocommit = 0;
	REPEAT
			
			SET i = i + 1;
		INSERT INTO s2
		VALUES
			(
				( min_num + i ),
				rand_string1 ( 6 ),
				( min_num + 30 * i + 5 ),
				rand_string1 ( 6 ),
				rand_string1 ( 10 ),
				rand_string1 ( 5 ),
				rand_string1 ( 10 ),
			rand_string1 ( 10 ));
		UNTIL i = max_num 
	END REPEAT;
	COMMIT;
	
END // 
DELIMITER;

ストアドプロシージャを呼び出す

s1 テーブルデータの追加: 10,000 レコードの追加:

CALL insert_s1(10001,10000);

s2 テーブルデータの追加: 10,000 レコードの追加:

CALL insert_s2(10001,10000);

6.4 各EXPLAIN列の機能

1.テーブル

クエリステートメントがどれほど複雑であっても、クエリステートメントに含まれるテーブルの数がどれだけ多くても、最終的には各テーブルに 1 つのテーブルからアクセスする必要があるため、MySQL では、EXPLAIN ステートメントによって出力される各レコードが 1 つのテーブルアクセスに対応するように規定されています。、レコードのテーブル列は、テーブルのテーブル名を表します (実際のテーブル名ではなく、略語である場合もあります)。

2. ID

通常、作成するクエリステートメントは SELECT キーワードで始まります。次のクエリステートメントのように、比較的単純なクエリステートメントには SELECT キーワードが 1 つだけ含まれます。

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 = 'a';
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | s1    | NULL       | ref  | idx_key1      | idx_key1 | 303     | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 INNER JOIN s2;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+---------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                                 |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+---------------------------------------+
|  1 | SIMPLE      | s1    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | NULL                                  |
|  1 | SIMPLE      | s2    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | Using join buffer (Block Nested Loop) |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+---------------------------------------+
2 rows in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 IN (SELECT key1 FROM s2) OR key3 = 'a';
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
|  1 | PRIMARY     | s1    | NULL       | ALL   | idx_key3      | NULL     | NULL    | NULL | 9895 |   100.00 | Using where |
|  2 | SUBQUERY    | s2    | NULL       | index | idx_key1      | idx_key1 | 303     | NULL | 9895 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
2 rows in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 IN (SELECT key2 FROM s2 WHERE common_field
    -> = 'a');
+----+-------------+-------+------------+------+---------------+----------+---------+--------------------+------+----------+------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref                | rows | filtered | Extra                              |
+----+-------------+-------+------------+------+---------------+----------+---------+--------------------+------+----------+------------------------------------+
|  1 | SIMPLE      | s1    | NULL       | ALL  | idx_key1      | NULL     | NULL    | NULL               | 9895 |   100.00 | Using where                        |
|  1 | SIMPLE      | s2    | NULL       | ref  | idx_key2      | idx_key2 | 5       | atguigudb1.s1.key1 |    1 |    10.00 | Using index condition; Using where |
+----+-------------+-------+------------+------+---------------+----------+---------+--------------------+------+----------+------------------------------------+
2 rows in set, 2 warnings (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 UNION SELECT * FROM s2;
+----+--------------+------------+------------+------+---------------+------+---------+------+------+----------+-----------------+
| id | select_type  | table      | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra           |
+----+--------------+------------+------------+------+---------------+------+---------+------+------+----------+-----------------+
|  1 | PRIMARY      | s1         | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | NULL            |
|  2 | UNION        | s2         | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | NULL            |
| NULL | UNION RESULT | <union1,2> | NULL       | ALL  | NULL          | NULL | NULL    | NULL | NULL |     NULL | Using temporary |
+----+--------------+------------+------------+------+---------------+------+---------+------+------+----------+-----------------+
3 rows in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 UNION ALL SELECT * FROM s2;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
|  1 | PRIMARY     | s1    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | NULL  |
|  2 | UNION       | s2    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
2 rows in set, 1 warning (0.00 sec)

ID が同じ場合はグループとみなされ、上から下へ順番に実行されます。
すべてのグループにおいて、id 値が大きいほど優先度が高く、最初に実行されます。
注意点: 各 ID 番号は独立したクエリを表しており、SQL ステートメント内のクエリの数は少ないほど良いです。

3. タイプの選択

ここに画像の説明を挿入します

mysql> EXPLAIN SELECT * FROM s1 INNER JOIN s2;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+---------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                                 |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+---------------------------------------+
|  1 | SIMPLE      | s1    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | NULL                                  |
|  1 | SIMPLE      | s2    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | Using join buffer (Block Nested Loop) |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+---------------------------------------+
2 rows in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 UNION SELECT * FROM s2;
+----+--------------+------------+------------+------+---------------+------+---------+------+------+----------+-----------------+
| id | select_type  | table      | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra           |
+----+--------------+------------+------------+------+---------------+------+---------+------+------+----------+-----------------+
|  1 | PRIMARY      | s1         | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | NULL            |
|  2 | UNION        | s2         | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | NULL            |
| NULL | UNION RESULT | <union1,2> | NULL       | ALL  | NULL          | NULL | NULL    | NULL | NULL |     NULL | Using temporary |
+----+--------------+------------+------------+------+---------------+------+---------+------+------+----------+-----------------+
3 rows in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 IN (SELECT key1 FROM s2) OR key3 = 'a';
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
|  1 | PRIMARY     | s1    | NULL       | ALL   | idx_key3      | NULL     | NULL    | NULL | 9895 |   100.00 | Using where |
|  2 | SUBQUERY    | s2    | NULL       | index | idx_key1      | idx_key1 | 303     | NULL | 9895 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
2 rows in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 IN (SELECT key1 FROM s2 WHERE s1.key2 =
    -> s2.key2) OR key3 = 'a';
+----+--------------------+-------+------------+------+-------------------+----------+---------+--------------------+------+----------+-------------+
| id | select_type        | table | partitions | type | possible_keys     | key      | key_len | ref                | rows | filtered | Extra       |
+----+--------------------+-------+------------+------+-------------------+----------+---------+--------------------+------+----------+-------------+
|  1 | PRIMARY            | s1    | NULL       | ALL  | idx_key3          | NULL     | NULL    | NULL               | 9895 |   100.00 | Using where |
|  2 | DEPENDENT SUBQUERY | s2    | NULL       | ref  | idx_key2,idx_key1 | idx_key2 | 5       | atguigudb1.s1.key2 |    1 |    10.00 | Using where |
+----+--------------------+-------+------------+------+-------------------+----------+---------+--------------------+------+----------+-------------+
2 rows in set, 2 warnings (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 IN (SELECT key1 FROM s2 WHERE key1 =
    -> 'a' UNION SELECT key1 FROM s1 WHERE key1 = 'b');
+----+--------------------+------------+------------+------+---------------+----------+---------+-------+------+----------+--------------------------+
| id | select_type        | table      | partitions | type | possible_keys | key      | key_len | ref   | rows | filtered | Extra                    |
+----+--------------------+------------+------------+------+---------------+----------+---------+-------+------+----------+--------------------------+
|  1 | PRIMARY            | s1         | NULL       | ALL  | NULL          | NULL     | NULL    | NULL  | 9895 |   100.00 | Using where              |
|  2 | DEPENDENT SUBQUERY | s2         | NULL       | ref  | idx_key1      | idx_key1 | 303     | const |    1 |   100.00 | Using where; Using index |
|  3 | DEPENDENT UNION    | s1         | NULL       | ref  | idx_key1      | idx_key1 | 303     | const |    1 |   100.00 | Using where; Using index |
| NULL | UNION RESULT       | <union2,3> | NULL       | ALL  | NULL          | NULL     | NULL    | NULL  | NULL |     NULL | Using temporary          |
+----+--------------------+------------+------------+------+---------------+----------+---------+-------+------+----------+--------------------------+
4 rows in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM (SELECT key1, count(*) as c FROM s1 GROUP BY key1) AS
    -> derived_s1 where c > 1;
+----+-------------+------------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
| id | select_type | table      | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra       |
+----+-------------+------------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
|  1 | PRIMARY     | <derived2> | NULL       | ALL   | NULL          | NULL     | NULL    | NULL | 9895 |    33.33 | Using where |
|  2 | DERIVED     | s1         | NULL       | index | idx_key1      | idx_key1 | 303     | NULL | 9895 |   100.00 | Using index |
+----+-------------+------------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
2 rows in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 IN (SELECT key1 FROM s2);
+----+--------------+-------------+------------+--------+---------------+------------+---------+--------------------+------+----------+-------------+
| id | select_type  | table       | partitions | type   | possible_keys | key        | key_len | ref                | rows | filtered | Extra       |
+----+--------------+-------------+------------+--------+---------------+------------+---------+--------------------+------+----------+-------------+
|  1 | SIMPLE       | s1          | NULL       | ALL    | idx_key1      | NULL       | NULL    | NULL               | 9895 |   100.00 | Using where |
|  1 | SIMPLE       | <subquery2> | NULL       | eq_ref | <auto_key>    | <auto_key> | 303     | atguigudb1.s1.key1 |    1 |   100.00 | NULL        |
|  2 | MATERIALIZED | s2          | NULL       | index  | idx_key1      | idx_key1   | 303     | NULL               | 9895 |   100.00 | Using index |
+----+--------------+-------------+------------+--------+---------------+------------+---------+--------------------+------+----------+-------------+
3 rows in set, 1 warning (0.00 sec)

4.タイプ☆

完全なアクセス方法は次のとおりです: system、const、eq_ref、ref、fulltext、ref_or_null、index_merge、unique_subquery、index_subquery、range、index、ALL。

システム

mysql> CREATE TABLE t(i int) Engine=MyISAM;
Query OK, 0 rows affected (0.05 sec)

mysql> INSERT INTO t VALUES(1);
Query OK, 1 row affected (0.01 sec)

次に、このテーブルにクエリを実行するための実行プランを確認します。

mysql> EXPLAIN SELECT * FROM t;
+----+-------------+-------+------------+--------+---------------+------+---------+------+------+----------+-------+
| id | select_type | table | partitions | type   | possible_keys | key  | key_len | ref  | rows | filtered | Extra |
+----+-------------+-------+------------+--------+---------------+------+---------+------+------+----------+-------+
|  1 | SIMPLE      | t     | NULL       | system | NULL          | NULL | NULL    | NULL |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+--------+---------------+------+---------+------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

定数

mysql> EXPLAIN SELECT * FROM s1 WHERE id = 10005;
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | s1    | NULL       | const | PRIMARY       | PRIMARY | 4       | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

eq_ref

mysql> EXPLAIN SELECT * FROM s1 INNER JOIN s2 ON s1.id = s2.id;
+----+-------------+-------+------------+--------+---------------+---------+---------+------------------+------+----------+-------+
| id | select_type | table | partitions | type   | possible_keys | key     | key_len | ref              | rows | filtered | Extra |
+----+-------------+-------+------------+--------+---------------+---------+---------+------------------+------+----------+-------+
|  1 | SIMPLE      | s1    | NULL       | ALL    | PRIMARY       | NULL    | NULL    | NULL             | 9895 |   100.00 | NULL  |
|  1 | SIMPLE      | s2    | NULL       | eq_ref | PRIMARY       | PRIMARY | 4       | atguigudb1.s1.id |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+--------+---------------+---------+---------+------------------+------+----------+-------+
2 rows in set, 1 warning (0.00 sec)

実行プランの結果から、MySQL は s2 を駆動テーブルとして、s1 を被駆動テーブルとして使用するつもりであることがわかります。s1 に焦点を当てたアクセス方法は eq_ref であり、s1 テーブルにアクセスするときにアクセスできることを示します。主キーの同等のマッチングを通じて。

参照

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 = 'a';
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | s1    | NULL       | ref  | idx_key1      | idx_key1 | 303     | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

ref_or_null

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 = 'a' OR key1 IS NULL;
+----+-------------+-------+------------+-------------+---------------+----------+---------+-------+------+----------+-----------------------+
| id | select_type | table | partitions | type        | possible_keys | key      | key_len | ref   | rows | filtered | Extra                 |
+----+-------------+-------+------------+-------------+---------------+----------+---------+-------+------+----------+-----------------------+
|  1 | SIMPLE      | s1    | NULL       | ref_or_null | idx_key1      | idx_key1 | 303     | const |    2 |   100.00 | Using index condition |
+----+-------------+-------+------------+-------------+---------------+----------+---------+-------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)

インデックスマージ

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 = 'a' OR key3 = 'a';
+----+-------------+-------+------------+-------------+-------------------+-------------------+---------+------+------+----------+---------------------------------------------+
| id | select_type | table | partitions | type        | possible_keys     | key               | key_len | ref  | rows | filtered | Extra                                       |
+----+-------------+-------+------------+-------------+-------------------+-------------------+---------+------+------+----------+---------------------------------------------+
|  1 | SIMPLE      | s1    | NULL       | index_merge | idx_key1,idx_key3 | idx_key1,idx_key3 | 303,303 | NULL |    2 |   100.00 | Using union(idx_key1,idx_key3); Using where |
+----+-------------+-------+------------+-------------+-------------------+-------------------+---------+------+------+----------+---------------------------------------------+
1 row in set, 1 warning (0.00 sec)

実行プランの type カラムの値から、index_merge であることがわかります。MySQL は、s1 テーブルでクエリを実行するためにインデックスマージを使用するつもりです。

unique_subquery

mysql> EXPLAIN SELECT * FROM s1 WHERE key2 IN (SELECT id FROM s2 where s1.key1 =
    -> s2.key1) OR key3 = 'a';
+----+--------------------+-------+------------+-----------------+------------------+---------+---------+------+------+----------+-------------+
| id | select_type        | table | partitions | type            | possible_keys    | key     | key_len | ref  | rows | filtered | Extra       |
+----+--------------------+-------+------------+-----------------+------------------+---------+---------+------+------+----------+-------------+
|  1 | PRIMARY            | s1    | NULL       | ALL             | idx_key3         | NULL    | NULL    | NULL | 9895 |   100.00 | Using where |
|  2 | DEPENDENT SUBQUERY | s2    | NULL       | unique_subquery | PRIMARY,idx_key1 | PRIMARY | 4       | func |    1 |    10.00 | Using where |
+----+--------------------+-------+------------+-----------------+------------------+---------+---------+------+------+----------+-------------+
2 rows in set, 2 warnings (0.00 sec)

インデックスサブクエリ

mysql> EXPLAIN SELECT * FROM s1 WHERE common_field IN (SELECT key3 FROM s2 where
    -> s1.key1 = s2.key1) OR key3 = 'a';
+----+--------------------+-------+------------+------+-------------------+----------+---------+--------------------+------+----------+-------------+
| id | select_type        | table | partitions | type | possible_keys     | key      | key_len | ref                | rows | filtered | Extra       |
+----+--------------------+-------+------------+------+-------------------+----------+---------+--------------------+------+----------+-------------+
|  1 | PRIMARY            | s1    | NULL       | ALL  | idx_key3          | NULL     | NULL    | NULL               | 9895 |   100.00 | Using where |
|  2 | DEPENDENT SUBQUERY | s2    | NULL       | ref  | idx_key1,idx_key3 | idx_key1 | 303     | atguigudb1.s1.key1 |    1 |    10.00 | Using where |
+----+--------------------+-------+------------+------+-------------------+----------+---------+--------------------+------+----------+-------------+
2 rows in set, 2 warnings (0.00 sec)

範囲

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 IN ('a', 'b', 'c');
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra                 |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
|  1 | SIMPLE      | s1    | NULL       | range | idx_key1      | idx_key1 | 303     | NULL |    3 |   100.00 | Using index condition |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)

範囲

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 > 'a' AND key1 < 'b';
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra                 |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
|  1 | SIMPLE      | s1    | NULL       | range | idx_key1      | idx_key1 | 303     | NULL |  369 |   100.00 | Using index condition |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)

索引

mysql> EXPLAIN SELECT key_part2 FROM s1 WHERE key_part3 = 'a';
+----+-------------+-------+------------+-------+---------------+--------------+---------+------+------+----------+--------------------------+
| id | select_type | table | partitions | type  | possible_keys | key          | key_len | ref  | rows | filtered | Extra                    |
+----+-------------+-------+------------+-------+---------------+--------------+---------+------+------+----------+--------------------------+
|  1 | SIMPLE      | s1    | NULL       | index | NULL          | idx_key_part | 909     | NULL | 9895 |    10.00 | Using where; Using index |
+----+-------------+-------+------------+-------+---------------+--------------+---------+------+------+----------+--------------------------+
1 row in set, 1 warning (0.00 sec)

全て

mysql> EXPLAIN SELECT * FROM s1;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
|  1 | SIMPLE      | s1    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

結果の値は最良から最悪まで次のようになります: system > const > eq_ref > ref > fulltext > ref_or_null > index_merge >unique_subquery > index_subquery > range > index > ALL より重要なものが抽出されます (上の図の青色を参照)。。SQL パフォーマンス最適化の目標: 少なくとも range レベルに達すること。要件は ref レベル、できれば consts レベルです。(Alibaba 開発マニュアルで必須)

5.可能なキーとキー

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 > 'z' AND key3 = 'a';
+----+-------------+-------+------------+------+-------------------+----------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys     | key      | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------+------------+------+-------------------+----------+---------+-------+------+----------+-------------+
|  1 | SIMPLE      | s1    | NULL       | ref  | idx_key1,idx_key3 | idx_key3 | 303     | const |    1 |     5.00 | Using where |
+----+-------------+-------+------------+------+-------------------+----------+---------+-------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

6.キーレン☆

mysql> EXPLAIN SELECT * FROM s1 WHERE key2 = 10126;
+----+-------------+-------+------------+-------+---------------+----------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+----------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | s1    | NULL       | const | idx_key2      | idx_key2 | 5       | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+-------+---------------+----------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

key_len の長さの計算式:

varchar(10)变长字段且允许NULL = 10 * ( character set：
utf8=3,gbk=2,latin1=1)+1(NULL)+2(变长字段)
varchar(10)变长字段且不允许NULL = 10 * ( character set：utf8=3,gbk=2,latin1=1)+2(变长字段)
char(10)固定字段且允许NULL = 10 * ( character set：utf8=3,gbk=2,latin1=1)+1(NULL)
char(10)固定字段且不允许NULL = 10 * ( character set：utf8=3,gbk=2,latin1=1)

7.参考文献

mysql> EXPLAIN SELECT * FROM s1 INNER JOIN s2 ON s1.id = s2.id;
+----+-------------+-------+------------+--------+---------------+---------+---------+------------------+------+----------+-------+
| id | select_type | table | partitions | type   | possible_keys | key     | key_len | ref              | rows | filtered | Extra |
+----+-------------+-------+------------+--------+---------------+---------+---------+------------------+------+----------+-------+
|  1 | SIMPLE      | s1    | NULL       | ALL    | PRIMARY       | NULL    | NULL    | NULL             | 9895 |   100.00 | NULL  |
|  1 | SIMPLE      | s2    | NULL       | eq_ref | PRIMARY       | PRIMARY | 4       | atguigudb1.s1.id |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+--------+---------------+---------+---------+------------------+------+----------+-------+
2 rows in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 INNER JOIN s2 ON s2.key1 = UPPER(s1.key1);
+----+-------------+-------+------------+------+---------------+----------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref  | rows | filtered | Extra                 |
+----+-------------+-------+------------+------+---------------+----------+---------+------+------+----------+-----------------------+
|  1 | SIMPLE      | s1    | NULL       | ALL  | NULL          | NULL     | NULL    | NULL | 9895 |   100.00 | NULL                  |
|  1 | SIMPLE      | s2    | NULL       | ref  | idx_key1      | idx_key1 | 303     | func |    1 |   100.00 | Using index condition |
+----+-------------+-------+------------+------+---------------+----------+---------+------+------+----------+-----------------------+
2 rows in set, 1 warning (0.00 sec)

8.行☆

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 > 'z';
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra                 |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
|  1 | SIMPLE      | s1    | NULL       | range | idx_key1      | idx_key1 | 303     | NULL |  364 |   100.00 | Using index condition |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)

9. フィルタリング済み

mysql> EXPLAIN SELECT * FROM s1 WHERE key1 > 'z' AND common_field = 'a';
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+------------------------------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra                              |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+------------------------------------+
|  1 | SIMPLE      | s1    | NULL       | range | idx_key1      | idx_key1 | 303     | NULL |  364 |    10.00 | Using index condition; Using where |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+------------------------------------+
1 row in set, 1 warning (0.00 sec)

10.おまけ☆

mysql> EXPLAIN SELECT * FROM s1 WHERE 1 != 1;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra            |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+
|  1 | SIMPLE      | NULL  | NULL       | NULL | NULL          | NULL | NULL    | NULL | NULL |     NULL | Impossible WHERE |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------+
1 row in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 WHERE common_field = 'a';
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | s1    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 9895 |    10.00 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT MIN(key1) FROM s1 WHERE key1 = 'abcdefg';
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                   |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------------------+
|  1 | SIMPLE      | NULL  | NULL       | NULL | NULL          | NULL | NULL    | NULL | NULL |     NULL | No matching min/max row |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT key1 FROM s1 WHERE key1 = 'a';
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key      | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------------+
|  1 | SIMPLE      | s1    | NULL       | ref  | idx_key1      | idx_key1 | 303     | const |    1 |   100.00 | Using index |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT * FROM s1 ORDER BY key1 LIMIT 10;
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------+
|  1 | SIMPLE      | s1    | NULL       | index | NULL          | idx_key1 | 303     | NULL |   10 |   100.00 | NULL  |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

mysql> EXPLAIN SELECT key1, COUNT(*) AS amount FROM s1 GROUP BY key1;
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key      | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | s1    | NULL       | index | idx_key1      | idx_key1 | 303     | NULL | 9895 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

EXPLAIN はさまざまなキャッシュを考慮しません
EXPLAIN は、クエリの実行時に MySQL によって行われた最適化作業を表示できません
EXPLAIN では、トリガー、ストアドプロシージャ、またはユーザー定義関数がクエリに与える影響については説明しません。
一部の統計は推定値であり、正確な値ではありません

7. EXPLAIN のさらなる使用

JSON 形式: EXPLAIN ワードと実際のクエリステートメントの間に FORMAT=JSON を追加します。

EXPLAIN FORMAT=JSON SELECT ....

mysql> EXPLAIN FORMAT=JSON SELECT s1.key1, s2.key1 FROM s1 LEFT JOIN s2 ON s1.key1 = s2.key1 WHERE s2.common_field is not null;
| {
    
    
  "query_block": {
    
    
    "select_id": 1,
    "cost_info": {
    
    
      "query_cost": "12762.60"
    },
    "nested_loop": [
      {
    
    
        "table": {
    
    
          "table_name": "s2",
          "access_type": "ALL",
          "possible_keys": [
            "idx_key1"
          ],
          "rows_examined_per_scan": 9895,
          "rows_produced_per_join": 8905,
          "filtered": "90.00",
          "cost_info": {
    
    
            "read_cost": "294.90",
            "eval_cost": "1781.10",
            "prefix_cost": "2076.00",
            "data_read_per_join": "15M"
          },
          "used_columns": [
            "key1",
            "common_field"
          ],
          "attached_condition": "((`atguigudb1`.`s2`.`common_field` is not null) and (`atguigudb1`.`s2`.`key1` is not null))"
        }
      },
      {
    
    
        "table": {
    
    
          "table_name": "s1",
          "access_type": "ref",
          "possible_keys": [
            "idx_key1"
          ],
          "key": "idx_key1",
          "used_key_parts": [
            "key1"
          ],
          "key_length": "303",
          "ref": [
            "atguigudb1.s2.key1"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 8905,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
    
    
            "read_cost": "8905.50",
            "eval_cost": "1781.10",
            "prefix_cost": "12762.60",
            "data_read_per_join": "15M"
          },
          "used_columns": [
            "key1"
          ]
        }
      }
    ]
  }
} |

1 row in set, 1 warning (0.00 sec)

          "cost_info": {
    
    
            "read_cost": "294.90",
            "eval_cost": "1781.10",
            "prefix_cost": "2076.00",
            "data_read_per_join": "15M"
          },

read_cost は次の 2 つの部分で構成されます。

IOコスト
行検出の CPU コスト × (1 - フィルター) レコード

ヒント: 行とフィルターは、前に紹介した実行プランの出力列です。JSON 形式の実行プランでは、行は rows_examined_per_scan に相当し、フィルターされた名前は変更されません。

eval_cost は次のように計算されます。

行の検出コスト × フィルターレコード。

prefix_cost は、s1 テーブルのみをクエリするコストです。つまり、read_cost + eval_cost
data_read_per_join は、このクエリで読み取る必要があるデータの量を示します。

s2 テーブルの「cost_info」部分は次のようになります。

          "cost_info": {
    
    
            "read_cost": "8905.50",
            "eval_cost": "1781.10",
            "prefix_cost": "12762.60",
            "data_read_per_join": "15M"
          },

s2 テーブルは駆動テーブルであるため、複数回読み取られる可能性があります。ここでの合計は、s2 テーブルに複数回アクセスした後の累積値read_costです。誰もが主に、内部の値が接続クエリ全体の推定コストを表すことを懸念しています。これは、s1 テーブルの単一クエリと s2 テーブルの複数のクエリ後のコストの合計です。eval_cost prefix_cost

8905.50+1781.1+2076=12762.6

8. MySQL 監視分析 view-sys スキーマ

ホスト関連: host_summary をはじめとして、主に IO 遅延情報がまとめられています。
Innodb 関連: innodb から始まり、innodb バッファー情報と innodb ロックを待機しているトランザクションに関する情報がまとめられています。
I/O 関連: io から始まり、I/O の待機と I/O の使用状況についてまとめています。
メモリ使用量: メモリから始まり、ホスト、スレッド、イベントなどの観点からメモリ使用量を表示します。
接続とセッションの情報: プロセスリストとセッション関連のビューは、セッション関連の情報を要約します。
テーブル関連: schema_table で始まるビューには、テーブルの統計情報が表示されます。
インデックス情報: 冗長なインデックスや未使用のインデックスを含む、インデックスの使用状況の統計。
ステートメント関連: ステートメントから始まり、フルテーブルスキャンの実行、一時テーブルの使用、ソートなどのためのステートメント情報が含まれます。
ユーザー関連: ユーザーで始まるビューは、ユーザーが使用したファイル I/O および実行ステートメントの統計をカウントします。
待機中のイベントに関する情報: 待機から始まり、待機中のイベントの遅延を示します。

8.1Sys スキーマビューの使用シナリオ

インデックスステータス

#1. 查询冗余索引
select * from sys.schema_redundant_indexes;
#2. 查询未使用过的索引
select * from sys.schema_unused_indexes;
#3. 查询索引的使用情况
select index_name,rows_selected,rows_inserted,rows_updated,rows_deleted
from sys.schema_index_statistics where table_schema='dbname' ;

テーブル関連

# 1. 查询表的访问量
select table_schema,table_name,sum(io_read_requests+io_write_requests) as io from
sys.schema_table_statistics group by table_schema,table_name order by io desc;
# 2. 查询占用bufferpool较多的表
select object_schema,object_name,allocated,data
from sys.innodb_buffer_stats_by_table order by allocated limit 10;
# 3. 查看表的全表扫描情况
select * from sys.statements_with_full_table_scans where db='dbname';

発言関連

#1. 监控SQL执行的频率
select db,exec_count,query from sys.statement_analysis
order by exec_count desc;
#2. 监控使用了排序的SQL
select db,exec_count,first_seen,last_seen,query
from sys.statements_with_sorting limit 1;
#3. 监控使用了临时表或者磁盘临时表的SQL
select db,exec_count,tmp_tables,tmp_disk_tables,query
from sys.statement_analysis where tmp_tables>0 or tmp_disk_tables >0
order by (tmp_tables+tmp_disk_tables) desc;

IO関連

#1. 查看消耗磁盘IO的文件
select file,avg_read,avg_write,avg_read+avg_write as avg_io
from sys.io_global_by_file_by_bytes order by avg_read limit 10;

Innodb関連

#1. 行锁阻塞情况
select * from sys.innodb_lock_waits;