sql-statement-lock-stats.md

title	summary
LOCK STATS	TiDB 数据库中 LOCK STATS 的使用概况。

LOCK STATS

LOCK STATS 语句用于锁定统计信息。

警告：

锁定统计信息目前为实验特性，不建议在生产环境中使用。

语法图

LockStatsStmt ::=
    'LOCK' 'STATS' TableNameList

TableNameList ::=
    TableName (',' TableName)*

TableName ::=
    Identifier ( '.' Identifier )?

示例

创建表 t，插入一些数据，在未锁定表 t 的统计信息的情况下成功执行 ANALYZE 语句。

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)

锁定表 t 的统计信息，执行 ANALYZE 语句，warning 提示跳过对表 t 的 ANALYZE。

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)

解锁表 t 的统计信息，成功执行 ANALYZE 语句。

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 兼容性

该语句是 TiDB 对 MySQL 语法的扩展。

另请参阅

• 统计信息
• UNLOCK STATS
• SHOW STATS_LOCKED