UNLOCK STATS
UNLOCK STATS is used to unlock the statistics of a table or tables.
Synopsis
- UnlockStatsStmt
- TableNameList
- TableName
UnlockStatsStmt ::=
'UNLOCK' 'STATS' TableNameList
TableNameList ::=
TableName (',' TableName)*
TableName ::=
Identifier ( '.' Identifier )?
Examples
Create table t, and insert data into it. When the statistics of table t are not locked, the ANALYZE statement can be successfully executed.
mysql> create table t(a int, b int);
Query OK, 0 rows affected (0.03 sec)
mysql> insert into t values (1,2), (3,4), (5,6), (7,8);
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> analyze table t;
Query OK, 0 rows affected, 1 warning (0.02 sec)
mysql> show warnings;
+-------+------+-----------------------------------------------------------------+
| Level | Code | Message |
+-------+------+-----------------------------------------------------------------+
| Note | 1105 | Analyze use auto adjusted sample rate 1.000000 for table test.t |
+-------+------+-----------------------------------------------------------------+
1 row in set (0.00 sec)
Lock the statistics of table t and execute ANALYZE. From the output of SHOW STATS_LOCKED, you can see that the statistics of table t have been locked. The warning message shows that the ANALYZE statement has skipped table t.
mysql> lock stats t;
Query OK, 0 rows affected (0.00 sec)
mysql> show stats_locked;
+---------+------------+----------------+--------+
| Db_name | Table_name | Partition_name | Status |
+---------+------------+----------------+--------+
| test | t | | locked |
+---------+------------+----------------+--------+
1 row in set (0.01 sec)
mysql> analyze table t;
Query OK, 0 rows affected, 2 warnings (0.00 sec)
mysql> show warnings;
+---------+------+-----------------------------------------------------------------+
| Level | Code | Message |
+---------+------+-----------------------------------------------------------------+
| Note | 1105 | Analyze use auto adjusted sample rate 1.000000 for table test.t |
| Warning | 1105 | skip analyze locked table: t |
+---------+------+-----------------------------------------------------------------+
2 rows in set (0.00 sec)
Unlock the statistics of table t and ANALYZE can be successfully executed again.
mysql> unlock stats t;
Query OK, 0 rows affected (0.01 sec)
mysql> analyze table t;
Query OK, 0 rows affected, 1 warning (0.03 sec)
mysql> show warnings;
+-------+------+-----------------------------------------------------------------+
| Level | Code | Message |
+-------+------+-----------------------------------------------------------------+
| Note | 1105 | Analyze use auto adjusted sample rate 1.000000 for table test.t |
+-------+------+-----------------------------------------------------------------+
1 row in set (0.00 sec)
MySQL compatibility
This statement is a TiDB extension to MySQL syntax.