[グローバル|セッション]バインディングを作成

このステートメントは、TiDB に新しい実行計画バインディングを作成します。バインドを使用すると、基になるクエリを変更することなく、ステートメントにヒントを挿入できます。

BINDINGはGLOBALまたはSESSIONベースのいずれかになります。デフォルトはSESSIONです。

バインドされた SQL ステートメントはパラメーター化され、システムテーブルに格納されます。 SQL クエリが処理されるとき、パラメーター化された SQL ステートメントとシステムテーブル内のバインドされた SQL ステートメントが一貫しており、システム変数tidb_use_plan_baselinesがON (既定) に設定されている限り、対応するオプティマイザーヒントを使用できます。複数の実行計画が利用可能な場合、オプティマイザは最小コストで計画をバインドすることを選択します。

あらすじ

CreateBindingStmt
GlobalScope
BindableStmt

CreateBindingStmt ::=
    'CREATE' GlobalScope 'BINDING' 'FOR' BindableStmt 'USING' BindableStmt

GlobalScope ::=
    ( 'GLOBAL' | 'SESSION' )?

BindableStmt ::=
    ( SelectStmt | UpdateStmt | InsertIntoStmt | ReplaceIntoStmt | DeleteStmt )

例

mysql> CREATE TABLE t1 (
    ->  id INT NOT NULL PRIMARY KEY auto_increment,
    ->  b INT NOT NULL,
    ->  pad VARBINARY(255),
    ->  INDEX(b)
    -> );
Query OK, 0 rows affected (0.07 sec)

mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM dual;
Query OK, 1 row affected (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 8 rows affected (0.00 sec)
Records: 8  Duplicates: 0  Warnings: 0

mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 1000 rows affected (0.04 sec)
Records: 1000  Duplicates: 0  Warnings: 0

mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 100000 rows affected (1.74 sec)
Records: 100000  Duplicates: 0  Warnings: 0

mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 100000 rows affected (2.15 sec)
Records: 100000  Duplicates: 0  Warnings: 0

mysql> INSERT INTO t1 SELECT NULL, FLOOR(RAND()*1000), RANDOM_BYTES(255) FROM t1 a JOIN t1 b JOIN t1 c LIMIT 100000;
Query OK, 100000 rows affected (2.64 sec)
Records: 100000  Duplicates: 0  Warnings: 0

mysql> SELECT SLEEP(1);
+----------+
| SLEEP(1) |
+----------+
|        0 |
+----------+
1 row in set (1.00 sec)

mysql> ANALYZE TABLE t1;
Query OK, 0 rows affected (1.33 sec)

mysql> EXPLAIN ANALYZE SELECT * FROM t1 WHERE b = 123;
+-------------------------------+---------+---------+-----------+----------------------+---------------------------------------------------------------------------+-----------------------------------+----------------+------+
| id                            | estRows | actRows | task      | access object        | execution info                                                            | operator info                     | memory         | disk |
+-------------------------------+---------+---------+-----------+----------------------+---------------------------------------------------------------------------+-----------------------------------+----------------+------+
| IndexLookUp_10                | 583.00  | 297     | root      |                      | time:10.545072ms, loops:2, rpc num: 1, rpc time:398.359µs, proc keys:297  |                                   | 109.1484375 KB | N/A  |
| ├─IndexRangeScan_8(Build)     | 583.00  | 297     | cop[tikv] | table:t1, index:b(b) | time:0s, loops:4                                                          | range:[123,123], keep order:false | N/A            | N/A  |
| └─TableRowIDScan_9(Probe)     | 583.00  | 297     | cop[tikv] | table:t1             | time:12ms, loops:4                                                        | keep order:false                  | N/A            | N/A  |
+-------------------------------+---------+---------+-----------+----------------------+---------------------------------------------------------------------------+-----------------------------------+----------------+------+
3 rows in set (0.02 sec)

mysql> CREATE SESSION BINDING FOR
    ->  SELECT * FROM t1 WHERE b = 123
    -> USING
    ->  SELECT * FROM t1 IGNORE INDEX (b) WHERE b = 123;
Query OK, 0 rows affected (0.00 sec)

mysql> EXPLAIN ANALYZE SELECT * FROM t1 WHERE b = 123;
+-------------------------+-----------+---------+-----------+---------------+--------------------------------------------------------------------------------+--------------------+---------------+------+
| id                      | estRows   | actRows | task      | access object | execution info                                                                 | operator info      | memory        | disk |
+-------------------------+-----------+---------+-----------+---------------+--------------------------------------------------------------------------------+--------------------+---------------+------+
| TableReader_7           | 583.00    | 297     | root      |               | time:222.32506ms, loops:2, rpc num: 1, rpc time:222.078952ms, proc keys:301010 | data:Selection_6   | 88.6640625 KB | N/A  |
| └─Selection_6           | 583.00    | 297     | cop[tikv] |               | time:224ms, loops:298                                                          | eq(test.t1.b, 123) | N/A           | N/A  |
|   └─TableFullScan_5     | 301010.00 | 301010  | cop[tikv] | table:t1      | time:220ms, loops:298                                                          | keep order:false   | N/A           | N/A  |
+-------------------------+-----------+---------+-----------+---------------+--------------------------------------------------------------------------------+--------------------+---------------+------+
3 rows in set (0.22 sec)

mysql> SHOW SESSION BINDINGS\G
*************************** 1. row ***************************
Original_sql: select * from t1 where b = ?
    Bind_sql: SELECT * FROM t1 IGNORE INDEX (b) WHERE b = 123
  Default_db: test
      Status: using
 Create_time: 2020-05-22 14:38:03.456
 Update_time: 2020-05-22 14:38:03.456
     Charset: utf8mb4
   Collation: utf8mb4_0900_ai_ci
1 row in set (0.00 sec)

mysql> DROP SESSION BINDING FOR SELECT * FROM t1 WHERE b = 123;
Query OK, 0 rows affected (0.00 sec)

mysql> EXPLAIN ANALYZE SELECT * FROM t1 WHERE b = 123;
+-------------------------------+---------+---------+-----------+----------------------+-------------------------------------------------------------------------+-----------------------------------+----------------+------+
| id                            | estRows | actRows | task      | access object        | execution info                                                          | operator info                     | memory         | disk |
+-------------------------------+---------+---------+-----------+----------------------+-------------------------------------------------------------------------+-----------------------------------+----------------+------+
| IndexLookUp_10                | 583.00  | 297     | root      |                      | time:5.31206ms, loops:2, rpc num: 1, rpc time:665.927µs, proc keys:297  |                                   | 109.1484375 KB | N/A  |
| ├─IndexRangeScan_8(Build)     | 583.00  | 297     | cop[tikv] | table:t1, index:b(b) | time:0s, loops:4                                                        | range:[123,123], keep order:false | N/A            | N/A  |
| └─TableRowIDScan_9(Probe)     | 583.00  | 297     | cop[tikv] | table:t1             | time:0s, loops:4                                                        | keep order:false                  | N/A            | N/A  |
+-------------------------------+---------+---------+-----------+----------------------+-------------------------------------------------------------------------+-----------------------------------+----------------+------+
3 rows in set (0.01 sec)

MySQL の互換性

このステートメントは、MySQL 構文に対する TiDB 拡張です。

[グローバル|セッション]バインディングを作成

あらすじ

例

MySQL の互換性

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