CREATE [GLOBAL|SESSION] BINDING
This statement creates a new execution plan binding in TiDB. Binding can be used to inject a hint into a statement without requiring changes to the underlying query.
A BINDING can be on either a GLOBAL or SESSION basis. The default is SESSION.
The bound SQL statement is parameterized and stored in the system table. When a SQL query is processed, as long as the parameterized SQL statement and a bound one in the system table are consistent and the system variable tidb_use_plan_baselines is set to ON (default), the corresponding optimizer hint is available. If multiple execution plans are available, the optimizer chooses to bind the plan with the least cost. For more information, see Create a binding.
Synopsis
- CreateBindingStmt
- GlobalScope
- BindableStmt
CreateBindingStmt ::=
'CREATE' GlobalScope 'BINDING' ( 'FOR' BindableStmt 'USING' BindableStmt
| 'FROM' 'HISTORY' 'USING' 'PLAN' 'DIGEST' PlanDigest )
GlobalScope ::=
( 'GLOBAL' | 'SESSION' )?
BindableStmt ::=
( SelectStmt | UpdateStmt | InsertIntoStmt | ReplaceIntoStmt | DeleteStmt )
Examples
You can create a binding according to a SQL statement or a historical execution plan.
The following example shows how to create a binding according to a SQL statement.
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)
The following example shows how to create a binding according to a historical execution plan.
mysql> CREATE TABLE t(id INT PRIMARY KEY , a INT, KEY(a));
Query OK, 0 rows affected (0.06 sec)
mysql> SELECT /*+ IGNORE_INDEX(t, a) */ * FROM t WHERE a = 1;
Empty set (0.01 sec)
mysql> SELECT plan_digest FROM INFORMATION_SCHEMA.STATEMENTS_SUMMARY WHERE QUERY_SAMPLE_TEXT = 'SELECT /*+ IGNORE_INDEX(t, a) */ * FROM t WHERE a = 1';
+------------------------------------------------------------------+
| plan_digest |
+------------------------------------------------------------------+
| 4e3159169cc63c14b139a4e7d72eae1759875c9a9581f94bb2079aae961189cb |
+------------------------------------------------------------------+
1 row in set (0.01 sec)
mysql> CREATE BINDING FROM HISTORY USING PLAN DIGEST '4e3159169cc63c14b139a4e7d72eae1759875c9a9581f94bb2079aae961189cb';
Query OK, 0 rows affected (0.02 sec)
mysql> SELECT * FROM t WHERE a = 1;
Empty set (0.01 sec)
mysql> SELECT @@LAST_PLAN_FROM_BINDING;
+--------------------------+
| @@LAST_PLAN_FROM_BINDING |
+--------------------------+
| 1 |
+--------------------------+
1 row in set (0.01 sec)
MySQL compatibility
This statement is a TiDB extension to MySQL syntax.