大事务检测能力

前提条件

• 内核2.0.39.230300及以上版本支持该功能。
• 需要根据以下条件设置对应的参数值为“ON”。
  • 内核版本小于2.0.45.230900时，需要确认“log-bin”参数值为“ON”。您可参考修改GaussDB(for MySQL)实例参数查看或修改参数值。
  • 内核版本大于或等于2.0.45.230900时，需要确认“rds_global_sql_log_bin”参数值为“ON”。

使用方法

1. 增加系统变量“rds_warn_max_binlog_cache_size”检测大事务。

   表1 参数说明

   参数名称	级别	描述
   rds_warn_max_binlog_cache_size	global	当大事务产生的Binlog超过该值时，则报WARNING提示客户。 默认值为：18446744073709547520 取值范围为：[4096，18446744073709547520]

   事务产生的Binlog大小超过rds_warn_max_binlog_cache_size时，为了提醒客户及时提交事务，系统会报WARNING到客户端。为了避免给客户端发送多个WARNING，限制事务中每个statement发送一次这个WARNING给客户端。

   当配置rds_warn_max_binlog_cache_size为40KB(40960)：

   mysql> CREATE TABLE t1 (
       -> a longtext
       -> ) DEFAULT CHARSET=latin1;
   Query OK, 0 rows affected (0.12 sec)
   
   mysql> show variables like 'rds_warn_max_binlog_cache_size';
   +--------------------------------+-------+
   | Variable_name                  | Value |
   +--------------------------------+-------+
   | rds_warn_max_binlog_cache_size | 40960 |
   +--------------------------------+-------+
   1 row in set (0.01 sec)
   
   mysql> begin;
   Query OK, 0 rows affected (0.00 sec)
   
   mysql> INSERT INTO t1 VALUES (REPEAT('a',20000));
   Query OK, 1 row affected (0.01 sec)
   
   mysql> INSERT INTO t1 VALUES (REPEAT('a',20000));
   Query OK, 1 row affected (0.00 sec)
   
   mysql> INSERT INTO t1 VALUES (REPEAT('a',20000));
   Query OK, 1 row affected, 1 warning (0.00 sec)
   
   mysql> show warnings;
   +---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | Level   | Code | Message                             |
   +---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | Warning | 4008 | Recommend you to INSERT/UPDATE/DELETE rows in batches by multiple transactions. The current transaction required more than 'rds_warn_max_binlog_cache_size' (40960) bytes of storage. Which shall cause replication latency. Please commit it. |
   +---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   1 row in set (0.00 sec)
   
   mysql> select count(*) from t1;
   +----------+
   | count(*) |
   +----------+
   |        3 |
   +----------+
   1 row in set (0.01 sec)
   
   mysql> commit;
   Query OK, 0 rows affected (0.01 sec)
   
   mysql> select count(*) from t1;
   +----------+
   | count(*) |
   +----------+
   |        3 |
   +----------+
   1 row in set (0.01 sec)
   
   mysql> INSERT INTO t1 VALUES (REPEAT('a',50000));
   Query OK, 1 row affected, 1 warning (0.01 sec)
   
   mysql> show warnings;
   +---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | Level   | Code | Message           |
   +---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | Warning | 4008 | Recommend you to INSERT/UPDATE/DELETE rows in batches by multiple transactions. The current transaction required more than 'rds_warn_max_binlog_cache_size' (40960) bytes of storage. Which shall cause replication latency. |
   +---------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   1 row in set (0.00 sec)

2. 查看当前连接的事务Binlog cache大小。

   mysql> CREATE TABLE t1 (
   ->   a longtext
   -> ) ENGINE=InnoDB DEFAULT CHARSET=latin1;
   Query OK, 0 rows affected (0.10 sec)
   
   mysql> SHOW STATUS LIKE 'Rds_binlog_trx_cache_size';
   +---------------------------+-------+
   | Variable_name             | Value |
   +---------------------------+-------+
   | Rds_binlog_trx_cache_size | 0     |
   +---------------------------+-------+
   1 row in set (0.04 sec)
   
   mysql> begin;
   Query OK, 0 rows affected (0.00 sec)
   
   mysql> INSERT INTO t1 VALUES (REPEAT('a',20000));
   Query OK, 1 row affected (0.01 sec)
   
   mysql> SHOW STATUS LIKE 'Rds_binlog_trx_cache_size';
   +---------------------------+-------+
   | Variable_name             | Value |
   +---------------------------+-------+
   | Rds_binlog_trx_cache_size | 20150 |
   +---------------------------+-------+
   1 row in set (0.05 sec)
   mysql> commit;
   Query OK, 0 rows affected (0.00 sec)
   
   mysql> SHOW STATUS LIKE 'Rds_binlog_trx_cache_size';
   +---------------------------+-------+
   | Variable_name             | Value |
   +---------------------------+-------+
   | Rds_binlog_trx_cache_size | 0     |
   +---------------------------+-------+
   1 row in set (0.09 sec)

3. 查看当前所有连接的事务Binlog cache大小。

   mysql> SHOW GLOBAL STATUS LIKE 'rds_binlog_trx_cache_size';
   +---------------------------+-------+
   | Variable_name             | Value |
   +---------------------------+-------+
   | Rds_binlog_trx_cache_size | 40300 |
   +---------------------------+-------+
   1 row in set (0.05 sec)